KR20190089898A - METHOD AND MASK FOR MANUFACTURING WATERMARKED PAPER, METHOD OF MANUFACTURING OBTAINED WATERMARKED PAPER MASK, AND METHOD FOR AUTHENTICATING WRARMARKED PAPER - Google Patents

Abstract

A method of making a security paper comprising the steps of creating a watermark using a mask (10) attached to a wire of a papermaking machine, Wherein the elements are connected by linking elements (15), and wherein the light regions are pixels of a raster image And wherein the connecting elements are arranged such that at least some of the elements (18) for forming bright regions are in the form of raster images, which are seen as isolated pixels in transmitted light Lt; RTI ID = 0.0 > of < / RTI >

Description

METHOD AND MASK FOR MANUFACTURING WATERMARKED PAPER, METHOD OF MANUFACTURING OBTAINED WATERMARKED PAPER MASK, AND METHOD FOR AUTHENTICATING WRARMARKED PAPER

The present invention relates to a method for manufacturing watermarked security papers and to paper and documents thus obtained.

Watermarks have been used for a very long time in the field of security documents and can be used by changing the thickness of the paper substrate during fabrication by acting on the fiber deposition process and / .

There have been many improvements in the generation of watermarks.

More particularly, the present invention relates to a watermark for reproducing a halftone image.

Applicants' patent EP1122360 B1 and EP1252389 B1 describe methods for producing such a watermark, which is marketed by the applicant under the trade name Pixel Watermark. The mask used to manufacture such a watermark can be conveniently obtained by machining or chemical etching of the metal plate. This process makes it difficult to manufacture a high-precision mask because the spatial resolution of the details is at least 0.8 times the thickness, according to the rule of thumb. Thus, for a 0.5 mm thick mask, the apertures that can be created therein must have a size of at least 0.4 mm.

Other publications, WO2010 / 036104 A1, WO2011 / 117828 A1 or WO2011 / 081561 A1, also relate to the manufacture of watermarks of this type.

Patent application WO2013 / 140126 A1 discloses a watermark-forming mask in which a grid is formed with elements intended to form a pattern of watermarks. The regions formed by the elements in the watermark appear to be separated from each other, which is presented as an advantage when reproducing Arabic characters. This document does not address the problem of reproducing a raster image.

It is necessary to further improve the watermark which at least partly reproduces the raster image and the corresponding manufacturing method, especially the security provided by such watermark.

The present invention achieves this object by a method of manufacturing security paper, the method comprising:

Comprising the steps of creating a watermark using a mask fixed to a wire of a papermaking machine, the mask comprising elements (18) for forming light zones in the watermark, Wherein the elements are connected by linking elements, the bright regions being arranged as pixels of a raster image, the connecting elements being arranged in a matrix of the elements Is at least partially thin enough to lead to the formation of pixels of a raster image that appear as isolated pixels in transmitted light in naked eye.

"By the naked eye" or "by the naked eye" means observation by the human eye from a distance of 25 cm under normal daylight without daylight.

The present invention allows a visually appealing watermark to be created, and security against counterfeiting can be increased since the watermark is difficult to imitate due to its high sharpness.

Another advantage is that it allows for good dehydration of the paper during the formation of the paper.

In the prior art bridges or even frames are placed on a forming wire having relative positions corresponding to the pattern to be reproduced and held together with the various elements welded thereto so that when the watermark is visually observed Whilst in the present invention at least some of the elements of the watermark design appear to be separated from one another visually, which allows people to obtain notable new visual effects in the distance and to extend the range of patterns that can be created .

The visual impression of softness generated by the components of the pattern can be used to enhance the aesthetic appearance in particular. The watermark can be more easily recognized by people in the distance. Thus, instead of having the form of rasters of points connected at least partially together or of rasters of lines connected together, as in the case of a watermark of the current pixel type, the connection points are no longer visible or almost invisible It is possible to obtain a new type of watermark having a cloud or a cloud of lines.

Another subject of the present invention is a watermark-forming mask for implementing a method according to the present invention, comprising a set of elements for forming light zones, Elements are connected by linking elements and arranged as pixels of a raster image, for example, inferences of lines called "intaglio" lines in the banknote field, The connecting elements being sufficiently thin so that they are not visually visible in the watermark and the elements for forming the bright areas are arranged in the form of isolated pixels in the image in naked eye from transmitted light, Leading to the formation of pixels of the raster image as seen in isolated pixels.

Raster image

A "raster image" should be understood as an image formed by pixels disposed in a raster with variable spacing and / or size to produce a halftone image. A number of "grayscale levels" can be reproduced according to the density, size, height and / or amplitude of the pixels, or even depending on the local opacity of the paper in each pixel. In this case, the gray scale levels preferably produce a three-dimensional effect, for example a relief effect.

The raster image preferably represents a monument, landscape, animal, plant, or portrait. In particular, raster images can only represent monuments, landscapes, animals, plants, or parts of portraits.

As a variant, the raster image may in particular represent any geometrical shape forming part of the background of a background or other image, for example a monument, landscape, animal, plant or portrait. According to this modification, the raster image can be made to emphasize another image.

The pixels of the raster image can not be distinguished from each other, especially when the raster image is visually observed in the transmitted light. They can be distinguished from each other, especially when the raster image is magnified in transmitted light, for example, at least magnified by at least 10 times, preferably by at least 20 times magnification. Thus, they form a level 2 security characteristic.

According to one variant, the pixels of the raster image can be distinguished from one another when viewed visually in transmitted light, thereby forming a level-1 security characteristic.

Pixels

"Pixels" refer to individual elements in a pattern of watermarks, similar to pixels in a digital image.

The pixels may have any shape, but preferably have a dot shape, in particular a dot shape having a circular, elliptical or polygonal shape, or a shape of a line, or a character, an alphanumeric character, It can have the form of ideograms or symbols. The raster image may include pixels of various shapes.

The pixels form raster elements of the raster image.

The raster image may include pixels that are arranged in raster angles, i. E., Arranged in rows that make an angle with respect to the horizontal.

The thickness of the raster elements may be comprised between 200 and 1500 [mu] m.

In the case of pixels having the shape of a line, the width of the raster elements, i.e. lines, may be greater than 50 탆, in particular greater than 70 탆, preferably greater than 100 탆.

In the case of pixels having the form of dots, letters, alphanumeric characters or tablets, the maximum dimension of the raster elements, i. E. Excluding the thickness of the pixels, may be greater than 50 μm, in particular greater than 70 μm, preferably greater than 100 μm.

The raster image may be amplitude modulated, i.e. the pixels may be uniformly distributed and the size of the pixels may change, or may be frequency modulated, or even frequency and amplitude modulated. In particular, from some pixel sizes, the raster image can be amplitude modulated and frequency modulated below that pixel size.

The raster may be stochastic and may have a fixed pixel size, for example a statistical frequency varying to reproduce various gray scale levels. The pixels may have the same geometry depending on their amplitude, or, alternatively, the geometry of the pixels may vary with amplitude.

The arrangement of the pixels within the image is preferably automatically generated by the software package.

Mask

The mask can be made of any suitable material, especially metal and / or plastic.

The mask includes thin linking elements.

These connection elements, because of their thickness, leave little or no visible traces in the watermark, link the elements to form the visual pattern of the watermark, and correct the strength of the elements. The connecting elements preferably have a thickness comprised between 20 and 200 mu m, more preferably between 30 and 100 mu m. The thickness of the connecting elements is preferably constant.

The connecting elements preferably have a width comprised between 20 and 200 mu m, more preferably between 30 and 100 mu m. The width of the connecting elements is preferably constant.

The connecting elements preferably have a width and a thickness comprised between 20 and 200 mu m, more preferably between 30 and 100 mu m. The width and thickness of the connecting elements are preferably constant.

The connecting elements are preferably elongated elements.

The connecting elements are preferably arranged in a grid. In this case, the minimum dimension (l) of the cells of the grid may be larger than 300 mu m, especially between 300 mu m and 5 mm, preferably between 500 mu m and 3 mm.

The connection elements may be arranged between the base and the top of the elements for forming the bright areas to which they are connected. They are preferably disposed between or between the bases of the elements to form bright areas to which they connect.

The height of the elements to form bright areas may be constant throughout the mask. As a variant, in order to influence the formation of watermarks so as to obtain somewhat darker pixels in the transmitted light, the height of the elements for forming bright regions is variable throughout the mask.

The elements for forming the bright areas are preferably made of the same material as the connecting elements. In particular, the elements and connecting elements for forming bright areas preferably form integral parts, which provide a more rugged mask.

The mask comprises at least one region, elements for forming bright regions arranged as pixels of a raster image, and at least one region for forming another type of watermark, And may include areas that do not have elements for forming bright regions disposed as pixels of a raster image. Thus, at least one complete raster watermark and a multitone watermark obtained by a relief, such as embossment or electrotype watermarks, It is possible to obtain a watermark which is hybrid at some point due to overlapping and / or juxtaposition of the watermark of the watermark. These "hybrid" watermarks are particularly attractive from a visual point of view. Thus, the raster image of the watermark according to the invention can only form one part of the pattern, and the other part, in particular the complementary part, can be a different type of watermark, in particular a multi-tone watermark obtained by embossing. This is particularly advantageous when the watermark forms an image and preferably a monument, a landscape, an animal, a plant or a portrait, according to a first variant, the watermark according to the invention forms only a part of the image And the other part, in particular the complementary part, is formed by a different type of watermark, in particular a multitone watermark obtained by embossing, and according to a second variant, a multitone watermark obtained by embossing in particular, And the other part, in particular the part of the background or the background of the image, is formed by the watermark according to the invention. The portion formed by the watermark according to the present invention is used to emphasize or emphasize part or all of the other part of the watermark.

The mask may comprise a plurality of elements for forming bright regions, each of which is seen as an isolated pixel in the image, and preferably, in at least one region of the mask, The density of the elements for each pixel is comprised between 30 and 60 elements / cm < 2 >, for example, producing many isolated pixels in the resulting image.

The mask may comprise apertures for forming regions of clear regions disposed as pixels of the raster image in one region and regions darker than the bright regions in another region, The apertures are also arranged as pixels of the raster image. The two areas correspond to the dark and bright areas of the image, respectively. Between them, the watermark may include areas where pixels corresponding to bright regions are connected in the image and are no longer isolated. The darker areas may have the same opacity as the vellum zone and may even be treated as small areas of the bellum.

At least one of the elements for forming bright zones may have a maximum dimension comprised between 0.3 mm and less, in particular between 0.1 and 0.3 mm.

This level of detail is particularly advantageous because it makes it more difficult to imitate the watermark.

If the elements for forming the bright zones have a minimum dimension of, for example, a width of less than 1 mm, except for the thickness, to ensure dewatering during the production of paper, very small diameter holes of, for example, It is possible to do.

The elements for forming the bright regions may have a cross-section that undergoes amplitude modulation along the raster row of the image, which allows the variable-sized raster dots or lines to be reproduced, And / or a height undergoing amplitude modulation along the raster column of the image, which allows raster dots or lines with varying opacity to be generated. In the latter case, it is possible to change the opacity as well as the distribution of the pixels, thereby changing the brightness of the pixels in the transmitted light, which creates new possibilities in terms of the final appearance of the watermark.

The spatial frequency of the elements for forming bright regions may be constant along at least one raster of the image. The spatial frequency of the elements for forming bright regions may be variable along at least one raster of the image. In order to obtain the best rendering of the image, it is also possible to combine the amplitude modulation of the sections of the elements to form bright regions, the amplitude modulation of their heights and / or the modulation of their spatial frequencies.

Wire

The wire is part of a papermaking machine and serves to form a fibrous web by dewatering the suspension of papermaking fibers.

The wire may be a wire of a cylindrical mold or a Fourdrinier machine.

Preferably, the wire is a cylindrical-metal wire.

Advantageously, the wire comprises a housing oriented towards the exterior of the fibrous web in the suspension, and it is advantageous for the mask to be disposed within the housing. This allows the mask to be protected, facilitating the placement of the mask and optimizing the opacity of the watermark (distribution of dark / light areas). The housing may be formed by embossing the wire. Alternatively, the mask may be placed on the surface of the wire, not in the recess of the wire, or on the embossed portion of the wire.

The mask can be secured to the wire by any suitable means, for example welded to a wire, especially soldered, or even adhesively bonded, crimped or mechanically fixed.

The wire and mask may be fabricated such that the watermark includes at least one raster zone and one non-raster zone. This is a matter of, for example, the juxtaposition and / or overlapping of various types of watermarks, for example wires and embossing of the mask according to the invention described above.

The watermarks can be used in combination with other security measures such as security threads, security fibers or security flakes, which are introduced into the paper during or after the production of the paper. More generally, the watermarked paper according to the present invention may comprise, in addition to the watermark, any additional security measures. Of the additional security factors, some may be visually detected in daylight or artificial light without using any particular equipment. These security elements include, for example, colored flakes or fibers. These security elements are referred to as level 1 security elements.

Other types of additional security factors can only be detected using relatively simple equipment, such as an ultraviolet (UV) or infrared (IR) lamp or a magnifying glass. Such security elements include, for example, fibers, flakes, particles or microtext. These security elements are visible or invisible to the naked eye and emit when illuminated by, for example, a Wood's ramp emitting at a wavelength of 365 nm. These security elements are referred to as level 2 security elements.

Other types of security elements require more complex detection equipment to be detected. These security elements may generate a particular signal, for example, when experiencing one or more external exciting sources concurrently or asynchronously. The automatic detection of the signal, if appropriate, verifies that the document is genuine. These security elements include, for example, tracers in the form of active materials, particles or fibers, which generate a specific signal when the tracer is subjected to excitation by optronic, electric, magnetic or electron. These security elements are referred to as level 3 security elements.

One or more additional security elements present in the paper according to the invention or in the secure document according to the invention may have security features of level 1, 2 and / or 3.

Another subject of the present invention is a method of manufacturing a mask according to the present invention wherein the elements for forming bright regions and optionally the connecting elements are fabricated using an additive method. This allows a higher resolution to be achieved than is possible with machining or chemical etching.

"Additive method" means the way in which the material is added, as opposed to how the material is removed, such as by machining or chemical etching.

Preferably, said elements for forming bright areas and, where appropriate, said connecting elements are made by electrodeposition, which allows a lower resolution to be achieved than chemical etching.

The connecting elements are preferably manufactured using the same additive method as the elements for forming the bright areas, so that they are integral with each other.

Electrodeposition, if desired, makes it easy to achieve a change in the amplitude of the height of the elements to form bright areas, and in order to provide a watermark with an additional "gray & Can be separated.

Electrodeposition allows the elements of the mask to be generated with high precision. It is possible to obtain an isolated pixel level detail of 0.1 mm size and it is also possible to vary the spacing between pixels to create a degrade. The detail value of 0.2 mm is particularly suitable for the resolution allowed by the paper substrate. The largest elements preferably have a size of 0.8 mm or less. Beyond this value, the elements are preferably made to have very small drain holes, e.g., holes having diameters comprised between 0.2 and 1 mm.

The finest details can be formed by bright areas in the watermark, in transmitted light.

Another subject of the invention is watermarked paper obtained in particular by carrying out the method defined above, which paper comprises a watermark with bright areas arranged as pixels of a raster image, The bright areas include at least one bright area that appears as isolated pixels in the image in transmitted light in naked eye. The watermark may include a number of such bright regions.

The watermark may include at least one region in which the pixels corresponding to the bright regions are no longer isolated and connected. The watermark may include at least one region with isolated pixels darker than the bright regions, and these dark pixels are disposed as pixels of the raster image.

The watermark is preferably formed of bright areas, which are arranged solely as pixels of the raster image.

The watermark may comprise a region having clear regions that are seen as isolated pixels in the transmitted light, wherein the density of the bright regions is comprised between 30 and 80 / cm 2, Occupies an area larger than 20 mm < 2 > in the watermark.

Another subject matter of the present invention is a method for authenticating watermarked paper in accordance with the present invention comprising the step of inspecting a watermark in transmitted light to detect the presence of a raster image, The pixels of a raster image appear as bright regions with at least one isolated pixel in the image and are preferably arranged in the image, particularly along the raster row of the image, It appears as bright areas with pixels.

The present invention can be used to produce any type of secure documents, such as banknotes, passports, and other identity documents or valuable documents.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention may be better understood by review of the following detailed description of non-limiting examples of practicing the invention and the accompanying drawings.
≪ RTI ID = 0.0 > 1A-1E < / RTI > show a detailed view of a watermark-forming mask according to the invention,
2A to 2C are cross-sectional views of examples of masks according to the present invention,
FIG. 3 shows an example of a mask according to the present invention,
Figure 4 shows the resulting image when the mask is viewed in transmitted light,
Figure 5 shows the detail of Figure 4,
5A and 5B show another example of the resultant image when viewed in the transmitted light, and the mask according to the present invention, respectively,
Figure 6 shows a mask according to the present invention placed in a housing of a wire.

Fig. 3 shows an example of the mask 10 according to the present invention. The mask includes linking elements 15 arranged in a grid, for example grid cells of a regular cross-section of square or rectangular shape in the example shown, I have. As a variant, the connecting elements 15 are not arranged in a grid.

1A shows an example of a mask.

The connecting elements 15 connect the isolated elements 18 forming bright regions arranged as pixels of a raster image. The elements 18 for forming these bright areas have a maximum dimension w.

The elements 18 may be located anywhere along the intersections of the grid formed by the coupling elements 15.

Figures 1B-1E illustrate what can be used for pixels of image elements of a non-circular contour.

This may be polygon elements, for example, rectangular elements as shown in Fig. 1B, straight elements as shown in Fig. 1C, or L-shaped elements as shown in Fig. 1D. It is also possible to have elements 18 of different geometry in the same holding grid, as shown in Figure IE.

The minimum dimension (l) of the cells is, for example, larger than 300 mu m, particularly between 300 mu m and 5 mm, preferably between 500 mu m and 3 mm.

2a-2c, it can be seen that the thickness e _g of the connecting elements 15 is smaller than the thickness e _e of the elements 18 for forming bright areas. The connecting elements 15 may form strands that intersect at right angles. Some of the strands may be oriented parallel to the rasters of the image, and the spacing between the strands may match the spacing between the rasters of the image.

Height (e _e) of the element (18) for forming a bright zone as shown in Figure 2b and 2c may be variable throughout the mask (10). This allows higher or lower brightness pixels to be obtained, which increases the number of parameters that can change for the purpose of reproducing the image. A change in the height of the elements 18 to form bright areas makes it possible to form a watermark that is more difficult to reproduce.

In the example shown in Figs. 2A-2C, the elements 18 for forming bright regions have a cross section that varies along rasters as a function of the size of the raster dots to be reproduced in the image, I have.

As shown in Figs. 2A-2C, the connecting elements 15 connect the bases of the elements 18 to form bright areas. As a variant, the connecting elements 15 connect the tops of the elements 18 to form bright areas.

The present invention is not limited to connecting elements 15 connecting the bases or tops of the elements 18 for forming bright areas. In particular, the connecting elements 15 may connect the elements 18 to form bright areas at points other than the base or top. As a variant, there is a need for a combination of various specific cases, such as connecting the elements 18 for forming bright areas through the base and / or upper and / or other points.

For example, as shown in Figures 4 and 5, certain elements 18 for forming bright areas of the mask may be formed in the acquired watermark 30 by isolating isolated pixels 20 And may appear to be broken bright areas. This is the case, for example, behind the hair.

The region 21 surrounding the pixels 20 may have the same thickness as the vellum zone 31. Fig. 6 shows that it is possible for the wire T accommodating the mask 10 to include the housing 100. Fig.

The mask 10 is disposed within the housing 100 and at least some of the elements 18 for supporting the connecting elements 15 against a flat bottom of the housing (Figure 6) Is supported against the flat bottom of the housing (100).

According to one variant, all the elements 18 and / or all the connecting elements 15 for forming bright zones are supported against the flat bottom of the housing 100. In particular, when the elements 18 for forming bright areas have a variable height, this configuration may be achieved, for example, by the housing 100, which is not planar, and / lt; RTI ID = 0.0 > relief. < / RTI >

The invention is not limited to the examples given.

In particular, one or more watermarks according to the present invention may be placed on paper to interact with other security elements, such as threads or foils.

The paper may be based on natural and / or synthetic fibers. Preferably, the paper comprises natural fibers such as linen and / or cotton fibers, in particular cotton linter.

The paper may be single-ply or multi-ply. In the case of multiple ply, the ply can be colored differently.

Claims (26)

A method of making a security paper comprising:
Comprising the step of generating a watermark using a mask (10) fixed to a wire of a papermaking machine,
Said mask comprising a network of elements (18) for forming light zones in said watermark, said elements being connected by linking elements (15) Are arranged as pixels of a raster image and the connection elements are arranged such that at least some of the elements (18) for forming bright regions are pixels isolated from naked eyes in transmitted light to the formation of pixels of a raster image as seen in isolated pixels. The method according to claim 1,
Wherein the pixels have the form of a dot, particularly a dot having a shape of a circle, an ellipse or a polygon. The method according to claim 1,
Wherein the pixels have the form of a line or have the form of a letter, an alphanumeric character, an ideogram or a symbol. 4. The method according to any one of claims 1 to 3,
Wherein the wire is a wire of a cylinder mold. The apparatus according to any one of the preceding claims,
Wherein the wire (T) comprises a housing (100) and the mask (10) is disposed within the housing. 6. The method of claim 5,
Wherein the housing is formed by embossing the wire. The apparatus according to any one of the preceding claims,
Wherein the mask is welded or brazed to the wire. 8. The method according to any one of claims 1 to 7,
Wherein the wire and the mask are fabricated such that the watermark comprises at least one raster zone and one non-raster zone. The apparatus according to any one of the preceding claims,
Wherein the height (e _e ) of the elements (18) for forming bright areas is constant throughout the mask. 9. The method according to any one of claims 1 to 8,
Wherein the height (e _e ) of the elements (18) for forming bright areas is variable throughout the mask. 11. A watermark-forming mask for performing the method according to any one of claims 1 to 10,
Includes a set of elements (18) for forming light zones,
The elements are connected by linking elements and are arranged as pixels of a raster image and the connecting elements 15 are thin enough to be visually invisible in the watermark, The elements for forming bright areas lead to the formation of pixels of a raster image that are visible as isolated pixels in the image from transmitted light to naked eye. 12. The method of claim 11,
The height of the elements (18) for forming bright areas is constant throughout the mask. 12. The method of claim 11,
Wherein the height of the elements (18) for forming bright areas is variable throughout the mask. 14. The method according to any one of claims 11 to 13,
Elements 18 for forming bright regions disposed as pixels of a raster image in at least one region and bright regions 18 arranged as pixels of a raster image, And at least one other region that does not have elements for forming the photomask. 15. The method according to any one of claims 11 to 14,
A plurality of elements (18) for forming bright regions, each of which appears as an isolated pixel in the image, and preferably, in at least one region of the mask, Wherein the density of the elements (18) is comprised between 30 and 60 elements / cm < 2 >. 16. The method according to any one of claims 11 to 15,
At least one of said elements (18) for forming bright areas has a maximum dimension (w) comprised between 0.3 mm and less, in particular between 0.1 and 0.3 mm. 17. The method according to any one of claims 11 to 16,
The elements (18) for forming bright regions have a cross section undergoing amplitude modulation along a raster row of the image. 18. The method according to any one of claims 11 to 17,
The elements (18) for forming bright zones have a height (e _e ) that undergoes amplitude modulation along a raster row of the image. 19. The method according to any one of claims 11 to 18,
The spatial frequency of the elements (18) for forming bright areas is constant along at least one raster of the image. 19. The method according to any one of claims 11 to 18,
Wherein the spatial frequency of the elements (18) for forming bright regions is variable along at least one raster of the image. 21. The method according to any one of claims 11 to 20,
Wherein the connecting elements (15) have a thickness (e _g ) comprised between 30 and 200 μm. 22. A method of manufacturing a mask according to any one of claims 11 to 21,
The elements 18 for forming bright areas leading to the formation of pixels of a raster image visible as isolated pixels in the image from the transmitted light to the naked eye, Wherein the mask is manufactured using an additive method. 10. A watermarked paper obtained by carrying out the method according to any one of claims 1 to 10,
A watermark having bright regions disposed as pixels of a raster image, wherein the bright regions are isolated pixels in an image in naked eye in transmitted light, Wherein the watermarked paper comprises at least one light area visible to the viewer. 24. The method of claim 23,
Wherein the watermark is formed only of bright regions disposed as pixels of a raster image. 25. The method according to claim 23 or 24,
The watermark includes a plurality of bright regions, each of which appears as an isolated pixel in the image. In particular, the watermark includes a region in which the density of bright regions that are seen as isolated pixels in the transmitted light is between 30 and 80 / Wherein the region preferably occupies an area greater than 20 mm < 2 > within the watermark. 25. A method for authenticating watermarked paper according to any one of claims 23 to 25,
And inspecting the watermark in transmitted light to detect the presence of a raster image,
The pixels of the raster image appear as bright regions with at least one isolated pixel in the image in the image and are preferably arranged in the image, particularly along the raster row of the image, Wherein the watermarked paper is visible in bright areas with isolated pixels of the watermarked paper.

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