MXPA01007402A - Printing of security documents. - Google Patents

Abstract

A method of printing a security document such as a banknote provides for the incorporation of identification features which are invisible to the eye but which are repeated over at least part of the surface of the document substrate to detection by an appropriately programmed computing device to authorise the document or to prevent its replication.

Description

Printing of security documents Field of the Invention This invention deals with the printing of security documents and in particular with printing and coding techniques which can be used to make it possible for an image-forming system based on a data processor to identify the presence of signals related to documents of security.

Background of the Invention It is known to scan a printed document and convert the image into digital data for feeding into a computer. A copy of the original document can be printed using the digital data of the images using a laser injection or inkjet printer, and in this situation, the imaging device (usually a scanning device), a computer and a printer They act like a copier. The stored data can be edited or manipulated using a logical equipment for graphics so that the final print can be a very accurate reproduction of the original. In addition, the data can be transmitted by REF: 131495 example by means of the Internet or by a Modem and a telephone line to a remote location, or stored for future use on a disk or other memory device, and this technology can be used for the forgery of security documents such as checks, bank notes, identification documents and the like.

Previous technique Methods for modifying substrates of documents are known so that genuine substrates can be identified and distinguished from counterfeit substrates. Typically, these methods include marking the genuine substrate with materials which are fluorescent under ultra-violet rays, or which only emit light in some special region of the visible spectrum, or involve the addition of a special material such as magnetic materials or pigments. absorption of infrared rays, or the inclusion of large-scale water marking in a pictorial or bar-coded form on or within the substrate. All these methods require either a total alteration of the substrate (as in watermarking methods) or the inclusion of special materials that usually require special detectors to determine if the substrate of any document is genuine. Such methods tend to be expensive, usually the effects are easily visible to the naked eye, and it is not impossible to modify the paper and other substrates in a similar way, to confuse a verification process.

Objective of the Invention It is an object of the present invention to provide a method for printing a security document with features which can be detected using a computer and another image-forming system based on a data processor, but which are non-aesthetically disturbing .

BRIEF DESCRIPTION OF THE INVENTION According to an aspect of the present invention, a method for printing a security document to enable authentication by a machine thereof includes the step of incorporating a plurality of identification features within the printout of the document so that when illuminates and images are formed on a photosensitive device, data signals are generated from the images at the output of the ». *.» ¿,.,. ^. 1 * device representative of the characteristics, characterized in that: 1. the contrast between the identifying characteristics and either the rest of the substrate surface or the rest of the printing in the regions containing the characteristics, is selected so that the image data signals corresponding to the characteristics are substantially indistinguishable from the data signals of the images related to the surface of the substrate or the surrounding image and / or the background noise signals; and they are due to that distinguishable by the eye; Y 2. the characteristics are repeated in a pattern on at least some of the surface of the substrate so that during imaging the position of the signals related to each characteristic will carry at least one fixed relation to the signals related to another characteristic, and the pattern that is such that a computational device supplied with the data signals of the images and programmed to perform the analysis of the images with the recognition of the pattern is able to determine whether the signals of the identification characteristics carrying at least one relationship fixed are i. < -. -.t present in the data, to generate due to that a signal identification of the document if the signals of the identification characteristics are found in the data signals of the images. Identification characteristics can be separated at regular intervals over the substrate area. Each of the printed identification features can be similar in particular to each of the other identification features. Documents of the same type can be printed with similar identification features that have a fixed, similar relationship on the surface of the document. In this way, for example, banknotes of a denomination can be printed having identification characteristics of a particular type and a unique particular separation for that denomination and value. The separation can be selected to be constant in one direction only, or varied according to a known special pattern. You can select similar or different separations for the identification characteristics in other directions by taking a spatial relationship, particular in relation to the first direction, for example perpendicular to the first direction. In a preferred example, the identification characteristics are arranged in a 2D matrix on the surface of the substrate. The existence of such printed identification features constitutes a primary coding of the substrate, which allows substrates to be distinguished from printed substrates that do not contain such characteristics, or which are distinguished from one another depending on the selection of features and / or separation . Secondary coding of a substrate can be achieved by introducing variations in the matrix such as by omitting characteristics of particular positions in such a regular matrix. In this way, for example, every fourth characteristic along each third line can be omitted. Preferably, secondary documents are encoded using both primary and secondary encodings. In addition or alternatively, secondary coding can be provided if the matrix is formed of features that have two particularities and, instead of omitting the characteristics in positions ^ y | ^ aa ^^^^ specific within the matrix, the characteristics of a type are located in a set of positions in the matrix and the characteristics of another type are located in other positions within the matrix. Thus, in a simple example, a feature set can be of generally circular shape, while the interleaved features can have a different easily distinguishable shape such as a rectangular or triangular shape. Since the coding of a printed substrate can be achieved by selecting the separation between the printed identification features, or selecting the features having a specific particularity such as the form which can be identified in the data signals of the images related to the same, and / or by the substitution in the selected points in a matrix that occurs regularly of the characteristics that have a particularity different from the other characteristics that form the matrix, and / or the omission of characteristics in particular points in a matrix, there is an almost infinite number of possible combinations and permutations available to encode the printed security documents. Therefore, the invention not only allows a reliable method for the identification of documents of »• * '* • - > • > - * security, for example to easily detect counterfeits which are not printed on an appropriate substrate, but each individual type of security document such as banknotes of different denominations, checks originating from different banks, passports issued by different offices, and the like, if desired may be uniquely identified by a particular primary and / or secondary coding of the printed material. Image analysis techniques to identify the presence of regularly occurring patterns and / or defects within regularly occurring patterns and / or shape (s) or color (s) or other visibly distinguishable features of the detectable identification features in an image, are readily available and known, and by the use of high-speed processors such as DSPs and the like, and image data can be checked and verified, or otherwise, be explored virtually instantaneously as printed documents . More preferably, if a secondary coding is present, any variation in the primary coding which constitutes the secondary coding is nevertheless capable of being distinguished by the naked eye or captured by a photosensitive device used t ^.,. ^,, «_.«. .. _ ^, ._. MÜUTA ^ ÜHMafcriiiáiÉÉ in a photocopier or document scanning device. Preferably, the coding of the printed identification features is in the form 5 of a repeating pattern. The coding or the pattern or both can be repeated at regular intervals in one or more directions throughout the document. When the identification characteristics are 10 such as the appearance of the printed security document (for example a bank note) is not affected or aesthetically disturbed, old, authentic security documents (especially bank notes) which do not contain the features encoded in 15 the printed material, are capable of being circulated in parallel with ones that contain the coding. Two or more different coding techniques that use the printed identification features can be combined in any document. The substrate may have a pattern printed therein using substantially transparent ink or ink whose color is substantially the same as the color of the substrate, so that when images are formed and converted into image data signals, the latter 25 which refer to the regions especially Printed labels are virtually indistinguishable, except for their particular relationship to other similar data signals, from the image data signals related to the rest of the substrate surface. Preferably, the printed pattern is a repeating pattern, which extends over some or all of the surface of the substrate. Where the printed pattern comprises primary coding and secondary coding, it produces 10 multiple iterations of a code in the substrate. The printed identification pattern can be extended only within one or more printed, selected areas of the document. The redundancy created by the multiple iterations can be used for benefit since the large number of similar iterations increases the detectability of the characteristics that make up the code by increasing the effective signal to the noise ratio. This facilitates the detection by the data processing apparatus 20 of the presence of an otherwise substantially invisible pattern of printed identification features. For a document identification system to work, the coding of documents must 25 being able to be read for example when scanning optically the documents and generate data signals from the images which can be handled by a computer, or when using an image formation and signal analysis device, specialist to perform this function. It is a feature of the proposal that while any printed marking that produces the coding of documents can be read and detected using a properly programmed data processing system, it is such that it is barely distinguishable by the naked eye and is also such that the signals The data from the images obtained from imaging and scanning of the document shall not contain data signals related to encoded marking of sufficient magnitude to reproduce the characteristics of the encoded marking in any subsequent printing process using the data signals, if they are used, for example, to control a laser, ink-jet or dye-diffusion printer. The invention is also found in a security document having a pattern of identification features encoded therein produced by the aforementioned method, the pattern being such that the data signals of the images representative of the pattern when the finished document is Illuminated can be recognized by a computer supplied with the data signals of the images and programmed to perform image analysis with pattern recognition. The invention is also found in a security document when printed as mentioned above. A primary application of the invention is found in the printing on the surface of a substrate of coding characteristics which if detected during a scanning or copying process 10 encourage a process of corruption or inhibition in copying / printing. The detection step is performed since the data signals of the images are obtained by scanning a document and digitizing the obtained signals and subjecting them to an algorithm. The invention also provides a method of document identification whereby for recognition purposes, a data processor may be programmed to search for one or more particular encodings which if detected in the data of the 0 images supplied to the processor as by the formation of images and the exploration of a document will generate a signal of identification of the document. This can be used for the validation of documents with images formed in the case of a banknote checking device, or inhibit or otherwise ^ Ék interfere with the printing of a replica of the document in other cases. In this way, the invention also provides a document scanning device based on a computer which can be used to identify the presence of a particular security document by verifying that one or more patterns of one or more features are present in The document. In this way, for example, the devices of The authentication of banknotes can be provided at a relatively low cost to be associated with the boxes in stores, banks and post offices, so that at the transition points the banknotes offered by the public can be verified before that these 15 be accepted. In the case of a value ticket or similar, it may be of additional interest to determine what denomination it is, and if more than one originating organization is involved, it may also be advantageous 20 determine which organization issued the ticket. The work teams for the verification of documents based on a computer of this type can be used as accepting devices of banknotes, can be used in cash desk and can be used to make ? * ¿¿¿Bi tf- ^ mn ^^^^ possible that blind people discover that bank notes have in their possession.

Description of the different printing coding techniques Any printing technique can be employed in general to produce a weak repeating pattern on the substrate such as a lithographic, dry transparency printing, letterpress printing, inkjet printing or electrophotographic transfer of ink or organic pigment. In one technique, a photographic matrix of the coding is formed into film such that the image is binary in nature. In other words, it has clear areas for the characteristics of the "images" and dark opaque areas for the "non-image" areas, or vice versa, and there are no "gray" areas. By this means, the pattern becomes a suitable way to form a printing plate. A secondary coding can be integrated into the print by introducing variations in the characteristics of the images and / or areas without images of the photographic matrix, typically by altering the signals which are used in the production of the photographic matrix. Using such a lithographic printing plate, the documentation substrate is first printed using a gray, yellow or very light brown ink which is very little different from the natural color of the substrate itself, so that the pattern in the document is substantially invisible naked eye. Alternatively, the ink may be added. 10 Some pigments such as reds, blues and greens can give a coloration to the substrate and this may be desirable in some documents. The term printing is also proposed to cover any technique in which the selected regions of A paper substrate is impregnated with a fluid such as a resin or lacquer such that the particularities of optical or reflectance absorption or the optical density of the substrate are sufficiently altered as between the impregnated or unimpregnated regions to be discele. 20 under incident light during scanning for digitization, and the selected and remaining regions comprise a pattern which constitutes a primary coding and variations in that pattern (such as edge, thickness and / or spacing variations) comprise 25 a secondary coding.

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Additionally, the surface of the substrate may be formed with the characteristics which produce different reflections of light than the rest of the surface. Different treatment of the surfaces can be used such as: (1) Embossed In a first technique that includes the invention, the substrate can be embossed during its manufacture. In this way, it is customary in the manufacture of paper or sheet plastics to make the material sufficiently smooth for printing by passing it through a high-pressure contact line between two steel rollers, a pss known as satin. By forming one or both of these rollers with indentations, a paper or plastic substrate forced therebetween will be formed with a pattern of embossing corresponding to the indentations. By appropriately encoding embossed features, the substrate will be encoded as required by the invention, and can be detected by adequate illumination and converted to digital data signals by a scanning device for analysis by a data pssor. (2) Surface treatment of papers with lacquer Where a paper material or plastic substrate has a resin or lacquer or other material mixed thereto to provide a smooth surface for printing, a surface-coded structure can be formed such that the current surface of the substrate is sufficiently smooth to accepting the printing ink to make it possible for a security document to be printed therein, but at the same time containing a fine pattern of less smooth regions, which may be less responsive to the printing ink. (3) Impregnation The surface can also be modified by a technique in which selected regions of a substrate describe a pattern of repetition by being impregnated with a fluid such as a resin, or lacquer, such that the particularities of optical absorption or reflectance or optical density of the The substrate is altered sufficiently as between the impregnated and non-impregnated areas to be discernible under the incident light as during the scan for digitization. a £ ^^ Ú? a **. ^^ HÉ ^ (4) Treatment with laser beam The surface of the substrate can be etched by a laser beam, to produce cavities or notches in the surface to be printed (or pending printing). This technique itself leads to the production of very fine patterns on the surface of the substrate and since a laser beam can be modulated very precisely this can be used to introduce the depth modulation 10 into any such notches or cavities as well as or instead of the edge or thickness of the separation modulation. (5) Water Marking 15 Watermarks alter the thickness and / or texture of a substrate, the variations that may and / or may become visible under incident light and may be used to form the primary and / or secondary coding of the 20 invention. These can be formed in two ways. In the method for making the Fourdrinier paper, the wet paper is embossed using an embossing roller when it is being formed, to fix a mark on the paper corresponding to that. 25 embossed. Through the formation of engraving in teaj ^ MlaaftÉM > fatellMllMtj j »- -» t. * ^ < faith ",. . JM »U relief in a suitable repeat pattern which extends over the area of the fabric, in this way the paper can be coded with the watermark pattern. A second technique to form a watermark uses the commonly called cylinder-matrix method. In this method the watermark is formed by a cylindrical wire mesh in which "matrices" are printed in the form of images. During the manufacture of paper, the fibers increase to a greater or lesser degree in the matrices of the mesh and where the thickness of the paper is greater, this gives a darker effect when it observes in transmission that the regions which are thinner and therefore that seem more clear when observed in transmission. However, where any type of watermark is only visible in the incident light this can be used to provide the background coding required by the invention. According to the invention, any water marking technique can be used to apply a pattern on the surface of a substrate, especially a paper substrate, which is virtually imperceptible to the naked eye, but which will appear as a low contrast pattern. when subject to incident light as where a document is ordered for scanning and digitization.

The techniques so far described provide a substrate encoded on the surface which can be subsequently printed to form a security document. However, some of the coding techniques, for example embossing, may be applied after something or all of the printing of the document has occurred. For example, embossing can be applied after a title, or other text, or personal data for example in the case of an ID document has been printed on a smooth substrate and a coding of the surface formed as a step post-printing Coding by embossing can be achieved while printing at least some regions of a document. In this way, the coding of the surface can be imparted to the document by notching printing commonly referred to as "without ink", or notch printing with colorless ink. In such a method, an image is printed using a plate containing engraved areas, some of which are filled with ink and some of which are left blank in the case of ink-less notch printing. The engraved plate, inked as appropriate, is pressed under high pressure against the substrate to cause the ink to be transferred to the substrate. The substrate can be recorded in MMMÜÜiÍliMiÉ AMMMÉÉ relief with the engraved image, under the applied pressure, with parts of the substrate surface that are printed, and others only engraved in relief. Within the scope of the invention, the treatment of the surface of a substrate includes any technique that results in lighter and darker regions that are visible on the surface of a treated sheet of the substrate when they are illuminated for scanning. Either or both the primary and secondary coding may be in the form of a repeating pattern which are distinguishable under appropriate lighting to provide a detectable content in digital signals obtained by scanning. Coding by embossing and printing can be achieved simultaneously. In this way, the code can be imparted to the document by printing in notch with substantially colorless ink. In such a method, an image is printed using a plate containing engraved areas, which are filled with ink. The engraved plate is impregnated with ink as appropriate and then pressed under high pressure against the substrate to cause the ink to be transferred to the substrate. The substrate can be engraved in relief with the engraved image, under pressure applied, with printed parts and others left blank. ^ < ~ & Brief Description of the Drawings Figure 1 shows a substrate of a banknote with an image formed with bar code characteris in prac not discernible to the naked eye; Figure 2 shows an image of a banknote printed on the substrate; Figure 3 is a flow chart of process 0 for printing the characteris of the bar code on the substrate of the banknote; Figure 4 is a flowchart of the process for embossing the characteris of the bar code on the substrate; Figures 5 and 6 show the images of the banknote revealed by a computer code extraction routine; and Figure 7 is a flow diagram of a possible deflection routine. 0 Description of the Modality Production The process for printing the identification features on a substrate of a banknote (or other security document) will be clear from Figure 3 without further description. Similarly, an alternative process for embossing the identification characteris on the substrate from Figure 4 will be clear. The resulting substrate is shown in Figure 1, except that in prac the identification characteris, in this case a repetitive barcode pattern, would be invisible to the naked eye, either printed or embossed. The banknote is conventionally printed on the substrate and the result is shown in Figure 4. Since in practice the identification features are invisible to the naked eye, they are not aesthetically disturbing and do not affect the freedom of design of the image. of the banknote. However, it should be noted that the design of the banknote can be printed either before or after the identifying characteristics are formed, either by printing (Figure 3) or by embossing (Figure 4). - pnl i? i Üi l -ii ¡il-tH i > mili i,, t «^ lÉtfÉiáaáaiíhMrii ÉaMii ^ ^ * M ^^^ M ^^^ MMM ^^^^ M ^ iM ^ M ^ Detection There are several ways in which computer-based equipment can detect the identification characteristics mentioned above and two of these methods are described below. The document encoded when it is scanned on a computer is converted to a digital format. This typically means that the image is analyzed in red, green and blue channels for each element or pixel of the image. The color of the image element is assigned a value in each of these channels on a scale from 0 to 255 (8 bits) typically such that a full intensity is assigned to the value 255 and ^ without color 'the value 0. From this Thus, the bright white will be represented by all three channels that have the value 255 and black by a zero intensity has the value 0. When a real image, such as that of the printed banknote, is scanned in the system, most of the values of the pixels will be in a central region between say, 230 for the bottom of the paper and 40 for the darker impression. The pixels related to the low contrast coding would be within a band very close to the values of the paper background. For example, assume that the coding is such that it is printed l .- «.-» - ".nfr .l» .. in a controlled manner so that it is always within a band of pixel values of 20 of the paper background. It is a simple issue for a computer program to restore all values between a value just below that of the paper (in this example, say 228), and the background of the values related to the coding band (in this example, say, 210). ) to a value of 10, or even zero, (almost black) and restore all other values between 210 and 0 in this example to 230 (in other words the same color as the paper background). This procedure has the effect of eliminating all printed design features except coding and those very weak features associated with the design, which are usually very few in number since they can not be easily seen and therefore would not be included in the design. the design for aesthetic reasons. The encoding itself by this procedure will now be converted to black (see Figure 5) so that it can be read by a program specially designed to recognize the encoding. As a simple example, if the encoding were a series of alphanumeric characters such as letters and numbers, an optical character recognition program could be used to read the data and determine if it was likely to be a known code. Alternatively, they could be i.i? • ^^^^^^^^ use the most sophisticated image detection techniques, especially if the coding was of a more complex type such as that used in digital watermarking for example. In some cases, it may be preferred in order to show the encoding only (Figure 6). Alternatively, the coding could be extracted using a contrast enhancement routine which is commonly known as "equalization". This is shown in Figure 7. This type of routine sets the maximum value of the pixels in each channel or 255 and the minimum value to 0 and then tries to uniformly redistribute the values of the pixels that intervene between the two. This has the effect of increasing the difference between the values of the pixels near the bottom of the paper and in this way those related to the code so that these are easier to recognize in an image recognition or routine program. This method has the disadvantage that other design features not related to the code are still present and need to be ignored by the recognition routine. However, you can use the more sophisticated routines with which you recognize complex coding patterns such as those used by ? t i il? *? * ?? ? *? fa? jMtt the high level codes in complex images and patterns.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. • - »* - * • * '

Claims (25)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A method for printing a security document to enable authentication by a machine thereof includes the step of incorporating a plurality of features. of identification within the printing of the document so that when it is illuminated and images are formed on a photosensitive device, data signals of the images at the output of the device representative of the characteristics are generated, characterized in that: (i) the contrast between the identification characteristics and either the rest of the substrate surface of the document or the rest of the printing in the regions containing the characteristics, is selected so that the data signals of the corresponding images the characteristics are substantially indistinguishable from the data signals of the images related to the surface of the substrate or the surrounding image and / or the background noise signals; and they are due to that distinguishable by the eye; Y ^^^ ^ ^^^ j ^ a ^ Éjj ^^ (ii) the characteristics are repeated in a pattern on at least some of the surface of the substrate so that during imaging the position of the signals related to each characteristic it will have at least one fixed relation to the signals related to another of the characteristics, and the pattern that is such that a computational device supplied with the data signals of the images and programmed to perform the analysis of the images with the recognition of the pattern is able to determine whether the signals of the identification characteristics carrying at least one fixed relation are present in the data, to thereby generate a signal identifying the document if the signals of the identification characteristics are found in the data signals of the images. 2. A method according to claim 1, characterized in that the identification characteristics are separated at regular intervals over the area of the substrate. 3. A method according to claim 1 or claim 2, characterized in that each of the printed identification features is similar in particular to each of the other identification features. t »i *« t? ..- C. -i, ^ .... «u-n ...-^^« -M.iiÉ «iMittMtfkÉ ^^. ^ a ^ M Étt 4. A method according to any of claims 1 to 3, characterized in that the separation of the identification characteristics is selected to be constant in a single direction, or varied according to a predetermined pattern, and similar or different separations are selected for the identification characteristics in other directions that carry a spatial relationship, particularly in relation to the first direction, for example perpendicular to the first direction. 5. A method according to any of claims 1 to 4, characterized in that the identification characteristics are arranged in a 2D matrix on the surface of the substrate. 6. A method according to claim 5, characterized in that the secondary coding of a substrate is achieved by introducing variations in the matrix such as by omitting the characteristics of particular positions in a regular matrix. A method according to claim 5, characterized in that the matrix is formed of characteristics that have two particularities and the characteristics of a type are located in a set of positions in the matrix and the characteristics ^ ¡^ ** ^^ of the other type are located in other positions within the matrix. A method according to any of claims 1 to 7, characterized in that two or more different coding techniques using the printed identification characteristics are combined in the substrate. 9. A method according to any of claims 1 to 8, characterized in that the substrate has printed thereon a pattern using a substantially transparent ink or an ink whose color is substantially the same as the color of the substrate, so that when images are formed and converted into data signals of the images , the latter which refer to the specially printed regions are virtually indistinguishable except for their particular relationship to other similar data signals, to the data signals of the images related to the rest of the substrate surface. 10. A method according to claim 9, characterized in that the printed pattern is a repeating pattern, which extends over some or all of the surface of the substrate. HriiiiiÉfta 11. A method according to claim 9 or claim 10, characterized in that the printed pattern comprising a primary coding and a secondary coding preferably produces multiple iterations of a code in the substrate. A method according to any of claims 9 to 11, characterized in that the printed identification pattern extends only within one or more selected printed areas of the document. A method according to any one of claims 1 to 12, characterized in that a printing technique is employed to produce a weak repetition pattern of the identifying characteristic on the substrate, such as a lithographic one, dry transfer printing, printing typographical, inkjet printing or electrophotographic transfer of ink or organic pigment. A method according to claim 13, characterized in that a secondary coding is integrated into the printing by introducing variations in the characteristics of the images and / or non-image areas of a photographic matrix, typically by altering the electrical signals which they are used in the production of the photographic matrix. »" - • »• '" "«' - »- * - • - '- - • - - - ~ - - .. | gg ^ | | ¡¡ 15. A method according to claim 13 or claim 14, characterized in that using a lithographic printing plate, the substrate of the document is first printed using a gray, yellow or brown ink of very light color which is very little different from the natural color of the substrate itself, so that the pattern of identification characteristics in the document is substantially invisible to the naked eye. 16. A method according to any of claims 1 to 15, characterized in that the surface of the substrate is physically formed with characteristics which produce different reflections of light than the rest of the surface. 17. A method according to claim 16, characterized in that the substrate is embossed during its manufacture to form the identification characteristics. A method according to claim 16, characterized in that a paper or plastic substrate material has a resin or lacquer or other material mixed therewith to provide a smooth surface for printing and a surface-coded structure is formed. such that the actual surface of the substrate is sufficiently smooth to accept the ink of ^ 2 ^^^ * ^^^^^^^^^^^^^^^^^ ° ^^^^^^^^^^^^^^ j ^^^^^^^^^^^ ^ ^ »^^^^^^^^^^^^ * ^^^^^^^^^ * t printing to make it possible for a security document to be printed on it, but at the same time it contains a fine pattern from less smooth regions, which are less receptive to the printing ink. 19. A method according to claim 16, characterized in that the surface of the substrate must be modified by a technique in which the selected regions of a substrate describe a repeat identification pattern when impregnated with a fluid such as a resin, or lacquer, such that the particularities of optical absorption or reflectance or optical density of the substrate are sufficiently altered as between the impregnated and non-impregnated areas to be discernible under incident light. A method according to claim 16, characterized in that the surface of the substrate is etched by a laser beam, to produce identification features in the form of cavities or notches in the surface to be printed (or pending printing). 21. A method according to claim 16, characterized in that water marking is used to vary the thickness and / or texture of a substrate, the variations that can and / or can be changed. j _ ^ _ visible under incident light and used to form the primary and / or secondary coding. 22. A substrate of the security document, characterized in that it has the identification features encoded therein, produced by the method of any of claims 1 to 21, the pattern that is such that the data signals of the representative images of the pattern when the finished document is illuminated can be recognized by a computer supplied with the data signals of the images and programmed to perform the analysis of the images with the recognition of the pattern. 23. A security document characterized in that it is printed with a superimposed design on the substrate of the document according to claim 22. 24. An identification method for the document of claim 23, characterized in that for the purposes of recognition, a processor Data is programmed to search for one or more particular encodings which, if detected in the data of the images supplied to the processor, such as by the image formation and the scanning of a document, will generate a document identification signal. 25. A method according to claim 24, characterized in that when it is used to validate the documents with images formed in the case of a banknote checking device, or to inhibit or otherwise interfere with the printing of a replica of the document in other cases.