WO2010028903A1 - Document, method for the production and verification of a document, computer program product, data processing system, and test system - Google Patents

Abstract

The invention relates to an ID document having optically detectable document-specific data (202) and an optically detectable representation (204) of a digital signature of the document-specific data.

Description

 Document, method of making and verifying a document, computer program product, data processing system and test system

Description

The invention relates to a document, in particular a value or security document, a method for producing a document, a method for checking a document, and corresponding computer program products and data processing systems and a test system.

Documents are already known from the prior art, which have an RFID chip, by means of which a cryptographic authentication can take place. For this purpose, reference is made, for example, to WO 2006/128829 A1.

The invention is based on the object to provide a document which can be authenticated using cryptographic methods, without necessarily a chip integrated into the document is required. It is a further object of the invention to provide a method of making such a document, a method of reviewing such a document, and corresponding computer program products, a data processing system, and a test system.

The objects underlying the invention are each achieved with the features of the independent claims. Embodiments of the invention are indicated in the dependent claims.

According to embodiments of the invention, a document with optically detectable individual document data is created. The document-specific data can be printed on the document in plain text and / or as a so-called machine readable zone (MRZ). The document-specific data may include personal data, ie data relating to the wearer of the Documents, such as name, address, gender, height, biometric data and / or data related to the document itself, such as the date of issue, validity (eg expiration date / expiration date) and / or issuing authority of the document.

The document also carries an optically detectable representation of a digital signature of the document-specific data. The optically detectable representation can be printed on the document or applied by means of another personalization technique. The representation can be a barcode, in particular a 2D barcode, a digital watermark or another pattern which can be read by machine using an optical sensor. In particular, the representation may be characters readable by means of Optical Character Recognition (OCR). The representation carries a digital signature of the document-individual data, which has been generated for example with the aid of a private key of a publisher of the document, or a protection of authenticity with symmetrical methods, for example a MAC.

Embodiments of the invention are particularly advantageous because the optically recordable representation printed on the document carries a digital signature which is usable for cryptographic authentication of the document. The digital signature is generated using a private key of an asymmetric cryptographic key pair. The digital signature may include a certificate, in particular a certificate of a PKI, which contains the public key belonging to the private key. Since no electronic circuit, such as an RFID chip, needs to be integrated into the document for a cryptographic authentication of the document, such a document can be manufactured correspondingly inexpensively.

A "certificate" is understood here to mean a digital certificate, which is also referred to as a public-key certificate, which is a structured data that serves to identify a public key of an asymmetric cryptosystem of an identity, such as a For example, the certificate may conform to the standard X.509 or another standard. A "document" here becomes an ID document, ie an identity document, such as an identity card, passport, driver's license or company identity card, or a means of identification such as a credit card, or other individualized credentials, such as The document may be paper and / or plastic-based, in particular the document may be book-like or card-shaped, and the document may be a chip card.

In particular, the document may be a so-called visa sticker, i. a visa document, which is intended for pasting into a passport.

According to one embodiment of the invention, the document carries an image, such as a passport photograph of a wearer of the document. The image may be printed on the document or applied by another personalization technique. During the production of the document, a so-called image hash is generated for this image.

To generate the image hash, use can be made of image-hashing methods which are known from the prior art. Image hashing is understood to mean the conversion of an image into a hash value, whereby two images that are visually identical or almost identical in appearance are very likely to have the same hash value. Such image hashing methods may be eigenvalue based or formed based on a discrete wavelet transform or as hashing via Singular Value Decomposition (SVD) method, cf. US 2007 02 39 756 A1; "Compact and Robust Image Hashing", Sheng Tang, Jin-Tao Li and Yong-Dong Zhang; "A New Fingerprinting Method for Digital Image", V. Fotopoulos and AN Skodras; "Content-based Image Authentication: Current Status, Issues, and Challenges", Han, Shuihua, Chu, Chao-Hsien, Yang, Shuangyuan, Semantic Computing, 2007. ICSC 2007, International Conference on Volume, Issue, 17-19 Sept. 2007, pp. 630-636; "Perceputal Image Hashing Via Feature Points: Performance Evaluation and Tradeoffs", Monga, V., Evans, BL; Image Processing, IEEE Transactions on, Vol. 15, Issue 11, Nov. 2006, pp. 3452-3465, M. Johnson and K. Ramchandran; "Dither-Based Secure Image Hashing Using Distributed Coding", Proc. IEEE Int. Conf. Image Processing, (Barcelona, Spain), September 2003.

An image hash is also referred to in the literature as an "image fingerprint".

According to embodiments of the invention, the image hash generated for the image of the document is combined with the document-individual data. This can be done by concatenating the image hash and the individual data of the document, or by another reversible operation applied to the image hash and the individual data of the document, e.g. by interleaving the image hash and the document-individual data or another combination operation. The combination generated from the image hash and the document-specific data is digitally signed and transformed into the optically detectable representation. In this embodiment, therefore, the document carries an image in addition to the document-specific data, the optically detectable representation bearing a signature of a combination of an image hash of this image and the data of the individual documents.

Such an embodiment is particularly advantageous because it provides a special level of security against manipulation of a document by exchanging the image. For example, if the passport photo is removed from a genuine ID document and replaced with a passport photo of another person, then a document check must fail because an image hash generated for the other person's passport photo is different from the image hash of the original passport photo.

According to one embodiment of the invention, one or more features are extracted from the image to produce the document. These features may be, for example, geometric features such as the position of the eyes, the eye relief, the position of the mouth, etc. in the image. Such features can be extracted manually, semi-automatically or fully automatically from the image, for example by means of suitable pattern recognition software. These extracted features are combined with the image hash. The combination of the extracted features with the image hash can be done, for example, by concatenation or other combination operation. The combination of the image hash and the at least one feature extracted from the image is also referred to as the "digital image seal." The digital image seal can in turn be combined with the document-specific data and the digital signature is generated for this combination The digital image seal has the advantage over the image hash that it is more robust to inaccuracies in the optical capture of the image data.

According to embodiments of the invention, the document-specific data comprise textual data, for example the data of a MRZ.

According to one embodiment of the invention, the optically detectable representation includes not only the signature but also the signed data itself, i. the document-individual data, the image hash, the at least one feature and / or the digital image seal. These data of the optically detectable representation can be included in the review of the document.

In a further aspect, the invention relates to a method for producing a document. According to embodiments of the invention, the production of a document takes place by the input of document-specific data into a data processing system, the generation of a digital signature for the document-individual data, for example by means of a private key, the transformation of at least the digital signature into an optically detectable representation and the application of the optically detectable representation on a document body. The application of the optically detectable representation can take place, for example, by printing technology or by means of another personalization technique on one of the layers of the document or on the document surface. For example, this will personalize a document blank. According to one embodiment of the invention, the document-individual data, the image hash, the at least one feature and / or the image seal and the digital signature are brought into a predefined data structure, for example by coding. This data structure is then transformed into the optically detectable representation. The data structure may be defined, for example, by Abstract Syntax Notation 1 (ASN.1).

According to one embodiment of the invention, the document-specific data or at least a subset of this document-specific data is digitally signed. This can be done so that a hash value is formed from the document-specific data. This hash value is encrypted using a private key of an asymmetric cryptographic key pair, resulting in the digital signature. This digital signature can be supplemented by the certificate of a PKI.

The digital signature is transformed into an optically detectable representation. Such a representation is understood to mean any form of opto-electronically readable presentation, such as a barcode, in particular a 2D barcode, a digital watermark or a representation which is suitable for OCR recognition.

According to one embodiment of the invention, a serial number of the document and / or data of the MRZ and / or an image of the document or its image HASH enter into the individual data of the documents, the individual data of the documents then being signed by asymmetric encryption with a private key become.

In a further aspect, the invention relates to a computer program product with executable program instructions for carrying out a method according to the invention for producing a document. For example, the computer program product serves to control a production facility for personalizing document blanks.

In a further aspect, the invention relates to a method for checking a document. According to embodiments of the invention, the check is carried out with the following steps: optical detection of individual document data and a representation of a digital signature of the document, reverse transformation of the representation to obtain the signature, verification of the signature for validity on the basis of the document optically recorded document data, generation of an output signal in response to a result of the verification of the signature.

In a further aspect, the invention relates to a computer program product with executable program instructions for carrying out an embodiment of a method according to the invention for checking a document. For example, the computer program product is designed to be executed by a test system, in particular a tester.

In a further aspect, the invention relates to a test system, in particular a test apparatus, for checking a document according to an embodiment of a method according to the invention.

In the following, embodiments of the invention will be explained in more detail with reference to the drawings. Show it:

FIG. 1 shows a flow chart of an embodiment of a method according to the invention,

FIG. 2 shows a schematic plan view of an embodiment of a document according to the invention,

FIG. 3 shows an embodiment of a method according to the invention for checking a document,

FIG. 4 shows a flowchart of an embodiment of a method according to the invention for producing a document,

FIG. 5 shows a schematic plan view of an embodiment of a document according to the invention, FIG. 6 shows a flowchart of an embodiment of a method according to the invention,

FIG. 7 shows a block diagram of an embodiment of a data processing system according to the invention,

FIG. 8 shows a block diagram of an embodiment of a test device according to the invention.

Elements of the following embodiments corresponding to each other are denoted by the same reference numerals.

FIG. 1 shows an embodiment of a method for producing a document. In step 100, individual document data is entered into a data processing system. The data processing system may be, for example, a control device of a personalization device for personalizing document blanks. The document-specific data may include, for example, textual data relating to the person of the document bearer and / or the document itself, such as name, place of residence, age, gender, size or date of issue, period of validity or issuing authority. In particular, the document-specific data may be the data of the so-called MRZ of an identity document, in particular according to ISO standards 1073-2: 1976 and ISO 183: 1980.

In step 102, the document-individual data entered in step 100 or at least a subset of this document-specific data is digitally signed. This can be done so that a hash value is formed from the document-specific data. This hash value is encrypted using a private key of an asymmetric cryptographic key pair, resulting in the digital signature. The digital signature is then transformed into an optically detectable representation in step 104. Such a representation is understood to mean any opto-electronically readable form of representation, such as for example, a barcode, especially a 2D barcode, a digital watermark, or a representation suitable for OCR recognition.

Optionally, the document-specific data themselves are transformed into the same or another optically readable representation. For example, for this purpose, the document-specific data are first combined with their signature, in particular concatenated, so that a bit string is obtained. This bit string is then transformed into the optically detectable representation so that it carries the individual data of the document as well as its signature.

In step 106, the document-specific data and the optically detectable representation are applied to the document, for example by printing the document-specific data in clear text on the document and also by printing the representation generated in step 104 on the document. The application of the data and representation in step 106 may be accomplished by means of per se known personalization techniques, such as typographical, laser personalization, or the like.

FIG. 2 shows an embodiment of a document 200 according to the invention, which can be produced according to the embodiment of the method of FIG. The document 200 has a first area 202 that carries document-individual data, such as textual data. The document 200 further has a region 204 which carries the optically detectable representation, which is embodied here as a 2D barcode. This embodiment of the document 200 is particularly advantageous for applications where the document needs to be of a particularly low price, such as for entrance tickets or other credentials. In particular, in this embodiment, the document 200 need not have an image of the wearer of the document.

FIG. 3 shows an embodiment of a method for checking the authenticity of the document 200.

In step 300, the textual data from region 202 and the representation from region 204 are optically acquired. This can be done with the help of a scan ners, a CCD camera or another optical sensor. For example, the entire front side of the document 200 is detected to automatically detect the areas 202 and 204 therein. For example, the location of the regions 202 and 204 in the document 200 may be predefined.

In step 302, the barcode of area 204 is back transformed so that the data previously transformed into the representation in step 104 is retrieved, i. For example, the textual data entered in step 100 and its signature (see Figure 1).

In step 304, it is checked whether the signature is valid. For this purpose, it is possible to proceed in such a way that a hash value is formed from the textual data of the representation according to the same hash method, which was used in step 102. The signature is decrypted using the public key associated with the cryptographic key pair so that the hash value generated in step 102 is recovered. If both hash values match, the signature is valid.

Subsequently, it is checked in step 308 whether the textual data acquired from region 202 coincides with the textual data obtained by reverse transformation from the barcode. If this is the case, a signal is generated in step 310 indicating the authenticity of the document. If, on the other hand, the signature is not valid, a signal is generated in step 306 which indicates that the document has been forged. Similarly, step 308 proceeds to step 306 if the textual data obtained by backtransforming the optical representation does not match the textual data acquired from region 202.

Alternatively, it is also possible to proceed in such a way that the textual data acquired from region 202 is used for checking the signature in step 304. From the textual data of the area 202, the hash value is then generated, which is compared with the hash value obtained from the signature by decryption with the public key. If the two hash values match, the signature is again valid. In this embodiment Step 308 may be omitted since the signature can only be valid if not only the private key used for the signature matches the public key used for the verification, but also the textual data acquired from the area 202 matches those which originally signed digitally in step 102.

FIG. 4 shows a further embodiment of a method according to the invention for producing a document. In this embodiment, a document is to be produced which has an image, such as a face image of the wearer of the document. In step 400, the image data is input to a data processing system. For example, the image is a digital photograph so that the image data is originally in a digital format. Alternatively, the photo is in a physical form, such as a paper print or imprint. In this case, the photograph is digitized with an optical sensor to capture the image data.

In step 402, an image hash of the image data is generated using an image hashing process. Optionally, one or more features may additionally be extracted from the image data. These may be geometric features, such as the position of the eyes, the distance between the eyes and the position of the mouth. These features are added to the image hash, for example by appending a corresponding bit string to the image hash, i. is confiscated. In this way, a so-called image seal is created, which is particularly meaningful with regard to the image data, and thus has a high degree of robustness against inaccuracies in the subsequent optical detection of the image data from the document.

In step 404, document-specific data, such as textual data, is entered into the data processing system. In step 406, the textual data and the image hash are combined. This can be done in such a way that a bit string representing the textual data and a bit string representing the image hash are concatenated or interleaved, for example by block-by-block data blocks of the textual data following data blocks of the image hash. In the event that from the image data in the step 402, one or more features have been extracted which have been combined with the image hash to form the image seal, then in step 406 a combination of the textual data with the image seal takes place, instead of just the image hash.

In step 408, the data combined together in step 406 is digitally signed. For example, for this purpose, a hash value is generated from the combination of the data, which is encrypted using a private key of a cryptographic key pair, from which the signature results.

In step 410, the textual data, the image hash and the signature are transformed into an optical representation, such as a 2D barcode. Before transformation, these data, i. the textual data, the image hash or the image seal, and the signature are converted into a predefined data structure, for example according to ASN.1. This predefined data structure is then brought into the optical representation for transformation of the data.

In step 412, the image data, the textual data, and the visual representation are applied to the document, such as by printing or other personalization technique, such as laser personalization.

FIG. 5 shows a corresponding embodiment of a document 200 which has been produced according to the method according to FIG. The document 200 has an area 206 carrying an embodiment of the image corresponding to the image data input or acquired in the step 400. This may be, for example, a facial image, in particular a passport photograph, of the wearer of the document 200. The document 200 may further include a so-called MRZ 208. Like the area 202, the MRZ 208 also carries textual data. At least part of this textual data may enter into the combination with the image hash or the image seal in step 406.

FIG. 6 shows a flowchart of a method for checking the authenticity of such a document 200. In step 500, the document 200 is detected by means of an optical sensor, such as an optical scanner or a CCD camera. The optical detection of the area 206 detects the image data of the image located there. From region 204, the optical representation, ie, for example, the 2D barcode, is detected. From the areas 202 and / or 208, the textual data are recorded, for example, by means of OCR.

In step 502, an image hash is generated from the image data. In step 504, the optical representation is retransformed, so that the transformation performed in step 410 (see FIG. As a result, the data processing system executing the method receives the textual data originally introduced into the optical representation, the image hash and the signature.

In an image seal embodiment, in step 502, the one or more features are extracted from the image data to obtain the image seal therefrom.

In step 506, it is checked whether the signature obtained by the inverse transformation in step 504 is valid. For this purpose, a public key belonging to the same asymmetric key pair as the private key used in step 408 is used. If the signature is not valid, a signal is output in step 508, after which the document is forged.

On the other hand, if the signature is valid, it is checked in step 510 whether the textual data acquired by the document in step 510 by OCR coincides with the textual data obtained in step 504 by backtransforming the optical representation. If this is not the case, it is again output in step 508 that the document is forged.

In the opposite case, it is checked in step 512 whether the image hash, which has been generated in step 502 from the optically acquired image data, matches the image hash obtained by inverse transformation in step 504. If this is not the case, it is output in step 508 that the document is forged; in the opposite case, it is output in step 514 that the document is real. In an embodiment with an image seal, it is checked in step 512 whether the image seal generated in step 502 coincides with the image seal obtained by inverse transformation in step 504.

FIG. 7 shows a data processing system 210 for producing a document 200. The data processing system 210 has a generator 212 for an image seal. The generator 212 has a program module 214 that implements an image hashing process. For example, the image hashing method is based on a principal component analysis.

Further, the generator 212 has a program module 216 which implements a feature extractor. The feature extractor is based on an image processing method for extracting one or more geometric features from the image. The image data may be input to the generator 212 in digital form. If the image is from a digital image source, the image data provided by the digital image source can be used immediately. Alternatively, the image may for example be in the form of an imprint from which the image data is obtained by scanning.

If the image data originates from an analog image source, the image data may be filtered prior to input to the generator 212, the filter altering the image represented by the image data when applied to the document and / or later optically capturing the image data from simulated the picture. For example, the image data is brought into a normalized form by the filter. The image data or the normalized image data are then input to the generator 212 so that an image hash of the image data is generated by the program module 214 and one or more features are extracted from the image data with the aid of the program module 216. The image hash and the at least one feature are then combined together, for example by concatenating the corresponding bit strings, so that the image seal is output at the output of the generator 212.

The data processing system 210 further has an MRZ generator 218 for generating the MRZ from textual input to the data processing system 210. In particular, data may include personal data relating to the carrier of the document 200.

The data processing system 210 further has a concatenator 220 for concatenating the image seal and the MRZ. For example, the image seal and the MRZ are output by the generator 212 and the MRZ generator 218 in the form of a bit string, respectively. By concatenator 220, these two bit strings are concatenated together. This results in a combined bit string.

The data processing system 210 further includes a signer 222 for generating a digital signature for the combined bit string output from the concatenator 220. For this purpose, the signer 222 has access to a private key which is assigned to the data processing system 210 or to an operator of this data processing system 210.

The data processing system 210 further has an encoder 224. The encoder 224 serves to first bring the data to be introduced into the optically detectable representation into a predefined data structure. Such a data structure may be specified using ASN.1. For example, the encoder 224 brings the digital signature generated by the signer 222 and the image seal provided by the generator 212 into the predefined data structure.

The data processing system 210 further includes an optically detectable representation generator 226. The generator 226 receives from the encoder 224 the predefined data structure that includes the digital signature and the icon seal. For this data structure, the generator 226 generates an optically detectable representation, such as a 2D barcode.

The data processing system 210 further has a generator 228 for a print file. The generator 228 receives the MRZ from the MRZ generator 218 as well as the optically detectable representation from the generator 226 and generates a print file therefrom. In addition, additional data can be included in the generation of the print file, such as the image data and other data. From the generator 228, a printer 230 or other personalization device is attached. controls to print a document blank 232 so that the personalized document 200 is obtained.

FIG. 8 shows a block diagram of a test system for checking the authenticity of the document 200. The test system may, for example, be designed as a test device 234 for a stationary or mobile use. The tester 234 may be connectable to or include an optical sensor 236.

The tester 234 has an inverse transformer 238 for inverse transforming the optical representation to undo the transformation performed by the generator 226 (see Figure 7). Further, the tester 234 has a decoder 240 which serves to undo the encoding performed by the encoder 224. The decoder 240 thus serves to recover the data contained in the predefined data structure.

The decoder 240 is connected to a concatenator 220 adapted to perform concatenation as well as to the concatenator 220 of FIG. 7. The tester 234 further includes an OCR module 242, which is also connected to the concatenator 220. An output of the concatenator 220 and the decoder 240 are connected to a signature verifier 244. It has access to a public key belonging to the same cryptographic key pair as the private key used by the signer 222.

The tester 234 further has a generator 212 with program modules 214 and 216, which in principle have the same operation as the generator 212 with these program modules in the embodiment of Figure 7. An output of the generator 212 is connected to a comparator 246, which also with an output of the decoder 240 is connected.

Furthermore, the test device 234 has an evaluation module 248 for evaluating the signals supplied by the comparator 246 and the signature verifier 244. The tester 234 further has an output 250 for outputting a result of the evaluation. The output 250 may be, for example, a display device, an acoustic output, and / or a machine interface. For example, a turnstile can be automatically released via the output 250 if the document 200 has been recognized by the tester 234 as genuine.

In operation, first the document 200 is optically detected by means of the optical sensor 236. The representation acquired from region 204 (see embodiment of FIG. 5) is input to the inverse transformer 238 and transformed back there. The inverse transformer 238 then outputs to the decoder 240 the data structure. This is decoded by the decoder 240. The image seal included in the data structure is input from the decoder 240 to the concatenator 220.

The data detected by the optical sensor 236 from the area 208 is input to the OCR module 242 to perform optical character recognition. Thereby, the MRZ is read from the document 200. The MRZ is input from the OCR module 242 into the concatenator 220. The concatenator 220 then concatenates the MRZ and the image seal provided by the decoder 240, as does the concatenator 220 in the embodiment of FIG. 7.

The concatenated bit string resulting from the concatenation of the MRZ and the icon is input from the concatenator 220 to the signature verifier 244. Furthermore, the signature verifier receives the digital signature obtained from the data structure from the decoder 240. The signature verifier then forms a hash value from the concatenated bit string and decrypts the digital signature with the aid of the public key. The hash value resulting from this decryption must match the hash value obtained from the concatenated bit string for the signature to be recognized as valid. The signature verifier 244 outputs a signal to the evaluation module 248 indicating whether the signature is valid or not. The generator 212 also inputs the image data acquired by the optical sensor 236 from the region 206. The generator 212 generates an image seal from the image data as well as the generator 212 in the embodiment of FIG. 7. The generator 212 outputs the image seal to the comparator 246.

The decoder 240 also outputs the image seal obtained from the data structure to the comparator 246. The comparator 246 compares the two image seals with each other. If the image seals match, it follows that the image captured by the document 200 has not been replaced by another one, which the comparator 246 signals to the evaluation module 248 with a first signal.

In the opposite case, the comparator 246 outputs a second signal. The evaluation module 248 then generates a first output signal which signals the authenticity of the document 200 when it receives the first signal from the comparator 246 and when the signature indicator 244 signals the validity of the signature.

In contrast, if the evaluation module 248 receives the second signal from the comparator 246 and / or signals from the signature verifier that the signature is not valid, then the evaluation module 248 generates a second output signal to indicate that the document 200 is forged. The first and second output signals are then output via the output 250 from the tester 234.

According to an alternative embodiment, instead of the image seal, the image hash is used directly, both by the data processing system 210 and by the tester 234. However, the use of the image seal is advantageous over the use of only the image hash since this reduces the robustness of the image hash Inspection against wear of the document 200, contamination or scratches of the document surface, inaccuracies in the optical detection or the like is increased. B ez inglese

200 document

202 area

204 range

206 area

208 MRZ

210 data processing system

10 212 generator

214 program module

216 program module

218 MRZ generator

220 concatenator

15 222 signers

224 encoders

226 generator

228 generator

230 printers

20 232 Document blank

234 testing device

236 optical sensor

238 reverse transformation

240 decoders

25 242 OZR module

244 signature verification

246 comparator

248 evaluation module

250 issue

30

Claims

Patent claims 1. ID document with optically recordable document-individual data (202) and an optically detectable representation (204) of a digital signature of the document-individual data. 2. ID document according to claim 1, wherein the optical representation is a barcode, in particular a 2D barcode, or a digital watermark, or wherein the optical representation is designed for optical character recognition. 3. ID document according to claim 1 or 2, wherein the ID document carries an image (206), wherein the digital signature is a signature of a combination of an image hash of the image and the document-individual data. The ID document of claim 1, 2 or 3, wherein the ID document carries an image, and wherein the digital signature is a signature of a combination of an image hash of the image, at least one of the image Image extracted feature and the document individual data. The ID document of claim 4, wherein the feature is a geometric feature. The ID document of any one of the preceding claims, wherein the document-specific data includes the data of a machine-readable line (208). 7. ID document according to one of the preceding claims, wherein the optically detectable representation includes the document-individual data and / or an image hash of an image of the document and / or at least one feature extracted from an image of the document. 8. A method of producing a document (200) comprising the steps of: Input of document-specific data, Generation of a digital signature of the document-specific data, Transformation of the digital signature into an optically detectable representation, visually recordable application of the individual data of the document and the representation on a document body. 9. The method of claim 8, further comprising the following steps: Acquisition of image data of an image applied or to be applied on the ID document, Generation of an image hash of the image from the image data, Generation of a combination of the image hash and the document-specific data, wherein the digital signature is a signature of the combination of the image hash with the document-individual data. 10. The method of claim 9, wherein at least one feature is extracted from the image data, wherein the feature is combined with the image hash and the document individual data, wherein the signature is a signature from the combination of the image hash , the at least one feature and the individual document data. 11. The method of claim 10, wherein the at least one feature is a geometric feature of the image. 12. The method according to any one of the preceding claims 8 to 11, wherein the document-individual data, the image hash, the at least one feature and / or the digital signature before the transformation into a predefined Data structure are brought, wherein the data structure is transformed into the representation. 13. computer program product with executable program instructions for carrying out a method according to one of the preceding claims 8 to 12. 14. Data processing system with: Means (222) for generating a digital signature of individual document data, Means (226) for transforming the digital signature into an optically detectable representation, Means (228) for optically detectable application of the document-individual data and the representation to a document body (232). 15. A method of reviewing a document (200) comprising the steps of: optically capturing document-individual data and a representation of a digital signature from the ID-document, - back transformation of the representation to obtain the signature, Checking the signature for validity on the basis of the document-specific data optically recorded by the ID document, Generation of an output signal as a function of a result of the verification of the signature. 16. The method of claim 15, wherein the ID document carries an image (206), the representation including a first image hash of the image, and wherein the signature is a signature of a combination of the image first image hash and the document-specific data, with the following additional steps: optically capturing the image from the ID document, Generation of a second image hash from the optically acquired image data of the image, Check if the first and second image hash match. 17. The method of claim 16, wherein the representation includes a first feature, wherein the digital signature is a signature of a combination of the first image hash, the first feature, and the document-individual data, wherein from the optically captured image data a second feature is extracted, and it is checked if the first and second features match. 18. The method according to any one of the preceding claims 15 to 17, wherein by backward transformation of the optical representation, a predefined data structure is generated, which includes the document-individual data, the first image hash, the first feature and / or the digital signature. 19. The method according to any one of the preceding claims 15 to 18, wherein the document-specific data data concerning the period of validity of the ID Documents, in particular an expiry date. 20. Computer program product with executable program instructions for carrying out a method according to one of the preceding claims 15 to 19. 21. Checking system for checking a document (200) with: Means (236) for optically capturing document-individual data and a representation of a digital signature from the ID-document, Means (238) for inverse transformation of the representation to obtain the signature, Means (244) for checking the signature for validity based on the document-individual data optically captured by the ID-document, Means (248) for generating an output signal in response to a result of the verification of the signature.