Classifications

• • G—PHYSICS
  • G07—CHECKING-DEVICES
  • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
  • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
  • G07D7/004—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency using digital security elements, e.g. information coded on a magnetic thread or strip
• • G—PHYSICS
  • G07—CHECKING-DEVICES
  • G07D—HANDLING OF COINS OR VALUABLE PAPERS, e.g. TESTING, SORTING BY DENOMINATIONS, COUNTING, DISPENSING, CHANGING OR DEPOSITING
  • G07D7/00—Testing specially adapted to determine the identity or genuineness of valuable papers or for segregating those which are unacceptable, e.g. banknotes that are alien to a currency
  • G07D7/005—Testing security markings invisible to the naked eye, e.g. verifying thickened lines or unobtrusive markings or alterations
  • G07D7/0054—Testing security markings invisible to the naked eye, e.g. verifying thickened lines or unobtrusive markings or alterations involving markings the properties of which are altered from original properties
  • G07D7/0056—Testing security markings invisible to the naked eye, e.g. verifying thickened lines or unobtrusive markings or alterations involving markings the properties of which are altered from original properties involving markings of altered colours

Definitions

• a method of preventing counterfeiting or altering a printed or engraved surface is a method of preventing counterfeiting or altering a printed or engraved surface.
• the present invention relates to a method for preventing counterfeiting or alteration of a printed or engraved surface.
• Special ink printing uses special chemical properties of the ink to provide a specific reaction to a particular action.
• fluorescent inks become very bright when they are lit by a particular wavelength, some inks are even invisible to natural light, other inks change color according to their orientation or their temperature (and can be reveal by heating the paper with a finger), etc.
• Special inks have one thing in common: particularly expensive and necessitate making modifications in the usual industrial production chain (additional mask for offset for example).
• additional mask for offset for example.
• Codes using invisible inks allow digital information to be hidden. These codes can be characters, bar codes, 2D codes, etc. In addition to its high cost and specific to invisible inks, this system has two major drawbacks. On the one hand, due to the nature of the codes used, it is located on a certain part of the document or of the packaging and it is therefore possible to destroy it without altering the entire surface. On the other hand, the codes used always have geometric characteristics (bars, geometric figures, characters, etc.) clearly identifying them as anti-copy devices. This greatly facilitates the task of the pirate seeking to reveal and reproduce the ink. In addition, as soon as the pirate knows how to make this reproduction, he ipso facto has the means to reproduce the code.
• systems based on on-board memories or processors combine the disadvantages of being very expensive, unattractive and localized. Their main application is more to secure a communication, or to dynamically store information rather than to distinguish an original from a copy.
• One of the aims of the present invention is to remedy the drawbacks of known methods making it possible to prevent counterfeiting or alteration of documents printed or engraved by digital means.
• the present invention relates to a method intended to prevent counterfeiting or alteration of printed or engraved documents characterized by the incorporation of a digital watermark in part or in the whole of the document.
• the digital watermark technique also known as digital watermarking, is a technique for hiding information in a robust and imperceptible way in multimedia data such as music, video, images, documents, etc.
• the information that is hidden is called the signature.
• This signature can for example be a number, a name or even an image.
• “Hide” has a very specific meaning in this context: for example in the case of an image, we will slightly change the color of certain pixels, and in the case of music we will slightly modify the sound from time to time.
• Imperceptible means that the changes introduced are such that an individual cannot distinguish the original data from the data signed by his own senses. For example, a signed image must have exactly the same appearance as a normal image, a signed music must appear completely normal, the same for a video or any other data. The whole problem is to make a computer capable of detecting this hidden information when it escapes our senses. There are also applications where a visible watermark is acceptable or even desirable. This allows in particular to further increase the robustness and a visual check for the presence of a watermark. The principle that remains is that the watermark should not be visually disturbing.
• the "robustness" of a watermark means that one must be able to find the signature after any manipulation of signed data. Take for example the case of a signed image: we must be able to compress, print, scan or rotate it without ever losing the signature.
• Many publications have been made on the various techniques allowing to hide a watermark in an image, in a video or an audio signal. With regard to images, the latter can be classified according to the technique used for marking: some operate modifications directly in the spatial domain (see for example [1] M. Kutter, F. Jordan, F. Bossen, "Digital watermaking of color images using amplitude modulation", Journal of Electronic Imaging, vol. 7, n ° 2, pp.
• the digital watermark technique has so far been used in order to find the signature on a possible copy to prove the origin of the information present on the copy, thanks to the presence of the watermark that the 'found on the copy. This in all cases involved the use of a robust watermark.
• the purpose of incorporating the digital watermark on the surface is different, since its presence is intended to prevent authentication or alteration of the surface concerned, i.e. provide proof that this is the authentic surface if the watermark is present or that it is a copy or that the surface has been altered if the watermark is missing.
• the robustness of the watermark must be reduced so that a copy of the surface results in a failure to read the watermark digital.
• a "fragile" watermark A typical example of application consists in preventing the counterfeiting of securities such as banknotes. If the watermark is incorporated to avoid alteration of all or part of the surface, the watermark may be strong or fragile.
• the watermark is printed using colors and resolutions that are invisible to the naked eye. This therefore makes it possible to protect, for example, a package without its graphics being altered, which is important for marketing reasons.
• the watermark can cover the entire surface of a printed document. It is therefore not possible to erase it without altering the document, for example by scratching the surface. In practice, this property makes it possible, for example, to avoid gray markets, ie products sold by unauthorized distributors. Indeed, they sometimes erase the code (invisible 2D code for example) identifying their reseller by "milling" the surface of the packaging where the code is printed. • Price
• the watermark is printed using traditional printing systems. Regarding industrial printing (offset, etc.), it is fully integrated into the production chain and does not incur any additional costs. Regarding personal printing (inkjet, laser, etc.), it is fully compatible with commercial printers. In both cases, the reading is done with a standard digital scanner. This low price opens up new markets: firstly for industrial printing, packaging for luxury or pharmaceutical products, as well as certificates, checks, entry tickets, etc. On the other hand for personal printing, it allows anyone with standard equipment to create and verify secure and personalized documents. For example, a doctor may hide the names of the drugs prescribed in the paper used to print the prescription. It is possible to program a printer so that it hides a watermark in any printed document thus allowing later identification of the date of printing, the name of the user, etc.
• the watermark contains digital information (typically several tens of bits per square centimeter) which is encoded or retrieved using a key.
• this storage makes it possible, for example, to secure information printed in visible text (therefore liable to be modified). Indeed it is then possible to encode the same information in the watermark and therefore to be able to detect any modification in the text of the document (date, amount, identity, etc.).
• One application concerns contracts for which we want to be sure of the date of issue.
• Another example with banknotes the serial number can be hidden in each note, so it is impossible to create counterfeit notes with different numbers because it would be necessary to generate each time the corresponding watermark.
• Figure 1 the graph shows the variation in luminance of the pixels of an image as a function of their X position and for an identical Y position. The four peaks illustrate the effect of a symmetrical modulation of this signal obtained by locally increasing or decreasing its intensity.
• the present invention proposes to asymmetrically modulate the color of the pixels.
• Figure 2 gives an example of asymmetric modulation obtained by darkening the color of certain pixels. This modulation can then be positive or negative depending on whether color is added or removed.
• the graph in the figure shows the variation in luminance of the pixels of an image as a function of their X position and for an identical Y position. The two peaks illustrate the effect of an asymmetrical modulation of this signal obtained by only decreasing its intensity.
• Figure 3 gives some examples of digital watermark images.
• Another object of the present invention is therefore to propose a method for hiding and / or finding a digital watermark, characterized by the use of an asymmetrical modulation of the amplitude of a visible or invisible light component.
• FIG. 1 illustrates an example of symmetrical modulation
• FIG. 4 illustrates the implementation of the integrated process with a standard offset printing technique
• FIG. 5 illustrates the implementation of the method with a separate offset printing step
• FIG. 8 is a block diagram of the process for signing a material in three stages
• - Figure 9 is a block diagram of the process for reading a uniform image signed in three stages; and - Figure 10 is a block diagram of the process for reading a non-uniform image signed in three stages.
• FIG. 1 An example of symmetrical modulation is illustrated in Figure 1.
• the graph shows the variation in luminance of the pixels of an image as a function of their X position and for an identical Y position.
• the four peaks illustrate the effect of a symmetrical modulation of this signal obtained by locally increasing or decreasing its intensity.
• FIG. 2 An example of asymmetric modulation is illustrated in Figure 2.
• the graph shows the variation in luminance of the pixels of an image as a function of their X position and for an identical Y position.
• the two peaks illustrate the effect of an asymmetrical modulation of this signal obtained by only decreasing its intensity.
• One way of obtaining a positive asymmetric modulation consists in using an overprinting technique by printing the watermark over the own colors of the material and other information already printed and therefore without taking account of local variations in the colors on the surface of this material.
• This approach requires that the values of the color components of the material can only be darkened during the signature since additional ink is added. Mathematically, this corresponds to a positive asymmetric modulation of the color of the points. In principle, this approach can be applied to any printing process. Some specifics of watermark printing may depend on the printing process. The specific cases of offset and inkjet type printing for achieving positive modulation are detailed below.
• Figure 4 illustrates the implementation of the above method using positive modulation with an industrial printing technique of offset type in the case of simultaneous printing of the watermark.
• a four-color printing 45 is carried out (for example for a packaging 40) which means that four different ink colors are used for each of the yellow masks 41, cyan 42, magenta 43 and black 44.
• the digital watermark can have a single color, it is generally desirable to use one of the colors already selected for standard printing for the watermark.
• Figure 4 shows how the different masks can then be applied.
• the watermark printing is fully integrated into the standard industrial printing chain and therefore does not incur any additional cost.
• the yellow mask can be used simultaneously for two different things: on the one hand it contains the yellow component of the image to be printed and on the other hand it contains the image of the watermark.
• the IT tools used when flashing the offset film make this integration easy.
• FIG. 5 Another possible alternative is to use a separate mask for the watermark as shown in Figure 5.
• the watermark is overprinted in an additional step with a mask and possibly its own ink (here magenta) .
• the mask 51 then defines the watermark points which are printed over the previously printed material 50.
• This method although more costly to implement by the printer, has the advantage of being able to easily change the watermark during the production. This allows for example to apply a watermark identifying different countries of sale to a series of identical packages. It should be noted that when non-covering inks are used, it is also possible to print the final image over the digital watermark, as illustrated in Figure 6. In this case, the reverse process is used.
• the watermark being previously printed 60 on the material, the final image being overprinted during an additional step.
• the masks yellow 61, cyan 62, magenta 63 and black 64 are used to overprint the pattern.
• the ink being transparent, the watermark 60 located under the pattern can still be detected in the final result 65.
• FIG. 7 Another usable printing method is of the inkjet type as illustrated in FIG. 7.
• the illustration shows an example of an inkjet printing system using four colors, yellow 71, cyan 72, magenta 73 and black 74, their print heads 75 and the printed material 70.
• the watermark is overprinted on the material. Setting up an inkjet printer for printing a watermark is particularly simple since the vast majority of printer drivers automatically manage the mixing of colors to obtain a particular shade. The four-color decomposition step is therefore most often unnecessary. It should however be noted that, depending on the drivers and printers, it may sometimes be desirable to choose a watermark color corresponding to the basic colors of the printer, this in order to avoid obtaining dithered colors or printing problems. alignment between dots of different colors.
• watermark printing can be simultaneous with the information or patterns intended to be printed normally. It is also possible to print the watermark separately, over or under the final design. In particular, text can be overprinted on the signed material itself, this text possibly being linked to the watermark. For example, the key figures of a contract can thus be hidden in the watermark of the paper and thus make it possible to guarantee its integrity.
• Negative modulation can be achieved during simultaneous printing by following the same principle as described above because it is always possible to subtract color from the electronic file: on the pattern to be printed, the points corresponding to the watermark are then cleared up.
• To achieve a separate printing with negative modulation it is however necessary to use a particular ink: for example, in the case of visible ink, one solution consists in using a covering type ink. The summary of different watermark printing possibilities is presented in the table below:
• Size of the points this is the diameter of the watermark points obtained after printing.
• the minimum dot size is set by printing technology. Values between 300 and 1200 dots per inch are common.
• Color of the points Depending on the color, texture and possible patterns applied to the materials, certain colors may be more or less visible. For example, it is usual to use a yellow color for white backgrounds (separate or simultaneous positive modulation).
• Density of the watermark This defines the ratio between the number of dots printed per unit area (also measured in dots). Typical values of 0.02 or less can be used. A very fine stitch size increases the density of the watermark.
• Screening The screening technique (halftone) makes it possible to reproduce any color from the different fundamental colors. It is then preferable that the size of the screening is sufficiently fine compared to the size of the points.
• Type of ink Non-visible substances can also be used.
• the influence of some of these parameters is illustrated in Figure 3.
• the watermark 1 is visible.
• the lower visibility of watermark 2 is obtained by simultaneously decreasing the density and size of the dots.
• the watermark 3 also has a clarification.
• the main difficulty lies in the ability to find the asymmetrical watermark.
• most tattoo techniques can extract information from the signed image without using the original image.
• Certain techniques first make a prediction of what the original image was from the signed image and can then deduce what the signature is. This technique is still applicable in the present case.
• the material has a uniform and known initial color, it is possible to suppress this prediction. This is particularly the case with a sheet of white paper.
• This increases the reliability of the detection and therefore reduces the visibility of the watermark up to the extreme limit of sensitivity of an optical scanner. Consequently, this makes it very difficult to duplicate the signed material, for example by photocopying: in fact, the losses specific to any reproduction system generally weaken this signature below the detectability threshold.
• One application is to include such a watermark on paper which one wishes to avoid copying, such as banknotes for example.
• One embodiment of the invention consists in using as a basis a digital watermark algorithm of the spatial type with symmetric amplitude modulation, such as for example that described in [1].
• c (k) ' c (k) + v.b.a (k) (1)
• Equation (1) the set of points defined by vba (k) constitutes the watermark ( Figure 8, step 84) which is added to the original image c (k) to give the signed image c (k ) It is the latter which is then printed according to the present invention.
• Equation 8 gives a block diagram of the complete method: the set of points constituting the watermark 85 is calculated 84 on the basis of the value of the bit to be hidden 81 and of the key 82 defining the random sequence a (k). The value of the points being positive or negative, as defined by equation (1). Equation (2) is equivalent to thresholding 86 the values of the watermark 85 while keeping only the positive values and then adding 88 these values 87 to the image to be signed 83 to obtain the signed image 89.
• this technique is qualified as “asymmetric amplitude modulation”.
• the sign of the modulation ba (k) being positive, the modulation is said to be positive.
• Equation (2) It is also possible to obtain a negative modulation by printing a uniform color or "pierced” by the watermark. Equation (2) then becomes:
• the new point value c (k) ' can be measured on the printed sheet using an optical scanner. Two cases then arise depending on whether the color of the material is uniform and known or not.
• Figure 9 is a block diagram describing the process: the signed image obtained by scanner is subtracted from the original image in order to restore the watermark. The bit constituting the signature is then calculated, optionally, an additional filtering step can be carried out if visible information has been printed over the signed uniform image. The signed image 91 is previously filtered 92 in order to eliminate any noise (scratches, dirt, text printed over the watermark, etc.).
• the image obtained 93 is then subtracted 94 from the original image 95 in order to extract the watermark 96.
• the value of bit b is then found according to conventional watermark detection techniques, as described in article [5] M . Kutter, "Watermarking resisting to translation, rotation, and scaling.”, Proceedings of SPIE International Symposium on Voice, Video, and Data Communications, November 1998, which consists essentially of reversing equation (2) and statistically correlating the value bit b found 99 on several pixels k in order to guarantee good robustness to possible errors which may for example arise during the digital acquisition of the image.
• This method can be generalized to several bits b and then makes it possible to code any digital information such as a number or a character string.
• the second case is illustrated by the block diagram of FIG. 10 where the original image is predicted from the signed image, the signed image is subtracted from the predicted image in order to restore the watermark, the bit constituting the signature is then calculated.
• a denoising filter 105 for example of the Wiener type, is used to make a prediction 106 of the original image o (k) from the signed image 101.
• the difference 102 between these two images then constitutes the watermark 107 which can be decoded 103 using the key 108 to find the bit 104 in the same way as before ( Figure 9).
• the prediction error being significantly greater than in the first case, the number of bits b coded in this way is systematically lower.
• the implementation of the detection requires an optical scanner capable of scanning the document on which the watermark is printed. Since positioning on the scanner is never perfect, it is necessary to be able to find the information coded by the watermark after possible translations and rotations.
• a suitable technique consists in using the method described by [5] which is based on an autocorrelated watermark (to compensate for rotations) and an intercorrelation technique (to compensate for translations).
• the process can also be applied to sectors other than printing.
• a laser to engrave metal surfaces, stones, ceramics, etc., and thus encode a digital watermark.
• the applications concerned are then, for example, parts from the automobile or aeronautical industry or luxury objects in the jewelry or objects sectors. of values.

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• Engineering & Computer Science (AREA)
• Computer Security & Cryptography (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Editing Of Facsimile Originals (AREA)
• Image Processing (AREA)
• Credit Cards Or The Like (AREA)
• Printing Methods (AREA)
• Dental Preparations (AREA)
• Paper (AREA)
• Treatments Of Macromolecular Shaped Articles (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Laminated Bodies (AREA)

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• 2001
  • 2001-09-17 US US10/380,914 patent/US7684088B2/en active Active
  • 2001-09-17 DE DE60143487T patent/DE60143487D1/de not_active Expired - Lifetime
  • 2001-09-17 DK DK01964793.2T patent/DK1319219T3/da active
  • 2001-09-17 WO PCT/CH2001/000560 patent/WO2002025599A1/fr active Application Filing
  • 2001-09-17 EP EP10174049.6A patent/EP2261867B1/de not_active Expired - Lifetime
  • 2001-09-17 EP EP01964793A patent/EP1319219B1/de not_active Expired - Lifetime
  • 2001-09-17 ES ES01964793T patent/ES2356598T3/es not_active Expired - Lifetime
  • 2001-09-17 CN CNB018188141A patent/CN1252653C/zh not_active Expired - Lifetime
  • 2001-09-17 AT AT01964793T patent/ATE488822T1/de active

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