AU2017367204B2

AU2017367204B2 - Two security features that together form a third security feature

Info

Publication number: AU2017367204B2
Application number: AU2017367204A
Authority: AU
Inventors: Frédéric Beauchet; Michel Blanc
Original assignee: Banque de France
Current assignee: Banque de France
Priority date: 2016-12-02
Filing date: 2017-12-04
Publication date: 2020-05-21
Anticipated expiration: 2037-12-04
Also published as: FR3059594B1; CA3045099A1; MY195594A; MX2019006335A; AU2017367204A1; EP3548298A1; EP3548298B1; WO2018100203A1; FR3059594A1; PL3548298T3; CA3045099C

Abstract

The invention concerns a set of N security features (105, 106, 110), each security feature forming, alone, an authentication feature different to those formed by the other security features, the different security features being shaped such that, when the N security features are superimposed, they together form an N+1th authentication feature (112) unrelated to the N other authentication features (107, 108, 111) each formed respectively by one of the N security features.

Description

TWO SECURITY FEATURES THAT TOGETHER FORM A THIRD SECURITY FEATURE

The invention concerns a set of at least two security symbols. The invention concerns in particular, although not exclusively, a set of two security symbols for protecting a security document such as a banknote or an identity paper or a bank card.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

In the field of security documents, and in particular of bills, it is known to secure the document using one or more security symbols.

It is therefore routine to provide a bill with a security symbol in two parts, a first part being inserted on the first face of the bill and a second part being inserted on the second face of the bill.

The first part of the security symbol is therefore observed when looking at the first face of the bill by reflection (that is to say by illumination of the first face of the bill without illumination of the second face). The second part of the security symbol is seen when looking at the second face of the bill by reflection (that is to say by illumination of the second face of the bill without illumination of the first face). On the other hand, if one of the faces of the bill is examined by transmission (that is to say with primary illumination of the non-examined face and secondary illumination of the examined face), the two parts of the security symbol are going to be visible through superposition because of the low opacity of the paper of the bill. The entirety of the security symbol can therefore be observed.

Bills in the eurozone typically include security symbols of this kind to form the numerical value of the bill.

This type of security symbol has the advantage of offering a good level of security because the two parts of

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PCT/EP2017/081336 the security symbol must be placed appropriately on the two different faces of the bill to be combined with each other, to form the security symbol. Moreover, this type of security symbol proves relatively simple for the general public to recognize without needing special equipment to detect a fraudulent bill.

Unfortunately, with technological advances, increasingly better performing machines are available on the market and hijacked by counterfeiters to reproduce bills fraudulently. Although these machines do not enable identical reproduction of this type of security symbol, they nevertheless enable more than correct reproduction that can fool many of the general public.

SUBJECT OF THE INVENTION

An aim of the invention is to propose a set of security symbols making it even more complicated to reproduce those security symbols fraudulently.

BRIEF DESCRIPTION OF THE INVENTION

To this end, the invention proposes a set of N security symbols, N being at least equal to 2, each security symbol forming on its own an authentication mark different from those formed by the other security symbols, the various security symbols being conformed to form conjointly by superposition of the N security symbols an N+l^th authentication mark unrelated to the other N authentication marks each formed by a respective one of the N security symbols.

As a result, not only does each symbol form an authentication mark but merely superposing the different symbols forms another additional authentication mark that is difficult to reproduce because it is unrelated to the other authentication marks and can moreover not be linked to any security symbol considered in isolation.

In particular, the N+l^th authentication mark is different from a simple combination of the other

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PCT/EP2017/081336 authentication marks, such as mutual juxtaposition, filling in, complementing with the other authentication marks.

As a result, with N security symbols at least N+l authentication marks are created, which renders the combination very secure.

Note therefore that the N+l^th authentication mark exists only through the superposition of the various security symbols and is therefore not linked to any tangible element, which makes it even more difficult to reproduce .

Moreover it advantageously proves relatively simple for the general public to detect counterfeiting because it suffices to superpose the two security symbols (for example by looking by transmission at the security set or by juxtaposing the security symbols) to be sure of the existence of the N+l^th authentication mark attesting to the validity of the whole.

In particular, the set comprises at least two security symbols, a first security symbol forming on its own a first authentication mark and a second security symbol forming on its own a second authentication mark different from the first authentication mark, the two security symbols being conformed to form conjointly by superposition of at least the two security symbols a third authentication mark unrelated to the first authentication mark and the second authentication mark.

In particular, each authentication mark forms on its own an identifiable image having an entirely distinct meaning.

The authentication mark can therefore be an alphanumeric symbol, a drawing, a geometrical figure, a barcode, etc.

In particular, at least two security symbols are carried by the same object.

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In particular, at least one of the security symbols is arranged on the first principal face of the object and at least one other security symbol is arranged on the second principal face of the object, the two symbols being arranged in the same portion of the object.

In particular, at least two of the security symbols are arranged on the same principal face of the object, folding the object enabling superposition of the two security symbols.

In particular, N is at least equal to 3.

In particular, the at least three security symbols are printed using inks having at least one absorption/excitation wavelength common to the three security symbols, the third security symbol furthermore being in an ink having at least one absorption/excitation wavelength that is specific to it and to which the other two security symbols do not react.

In particular, at least one of the security symbols is displayed on a device including a screen and at least one other security symbol is carried by an object.

In particular, at least one of the security symbols carried by an object is in an ink different from those of the rest of the object.

In particular, at least one of the security symbols is in an ink visible in daylight.

In particular, at least a first security symbol is printed using an ink having a first absorption/excitation wavelength and a second absorption/excitation wavelength and at least one second security symbol is printed over the at least one first security symbol in an ink having the first absorption/excitation wavelength and a third absorption/excitation wavelength different from the second absorption/excitation wavelength.

In particular, the at least one first security symbol and the at least one second security symbol are printed

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PCT/EP2017/081336 using inks that re-emit different colors in order for the N+l^th authentication mark to appear in a panel of colors comprising a color resulting from the combination of said colors of the at least one first security symbol and of the at least one second security symbol.

Features and advantages of the invention will emerge on reading the following description of particular nonlimiting embodiments of the invention.

DESCRIPTION OF THE FIGURES

The invention will be better understood in the light of the following description with reference to the figures of the appended drawings, in which:

- figure 1 is a highly diagrammatic sectional view of a document comprising a set according to a first embodiment of the invention,

- figure 2 is a top view of the document shown in figure 1 examined by reflection,

- figure 3 is a bottom view of the document shown in figure 1 examined by reflection,

- figure 4 is a top or bottom view of the document shown in figure 1 examined by transmission,

- figure 5 is a highly diagrammatic sectional view of a document comprising a set according to a second embodiment of the invention and a representation of the various security symbols examined in reflection and in transmission,

- figure 6 is a highly diagrammatic sectional view of a document comprising a set according to a third embodiment of the invention and a representation of the various security symbols examined in reflection and in transmission,

- figure 7 is a highly diagrammatic top view of a document comprising a set according to a fourth embodiment of the invention before and after folding the document,

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- figure 8 is a highly diagrammatic view of a document and a device equipped with a screen comprising a set according to a fifth embodiment of the invention,

- figures 9a to 9c are highly diagrammatic top views of an object comprising a set according to a sixth embodiment of the invention with the object illuminated differently.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring to figures 1 to 4, according to a first embodiment of the invention a document 1 such as a security document (bill, identity card, passport, bank card, etc.) or another type of document (lottery ticket, etc.) comprises a substrate 2 carrying a security set according to the first embodiment of the invention.

In the present embodiment, the same document 1 carries the security set and therefore here carries two security symbols .

In particular, the substrate 2 is conformed so that a first principal face 3 of the substrate 2 carries the first security symbol 5 and so that the second principal face 4 opposite the first principal face 3 carries the second security symbol 6. Here the two security symbols 5, 6 are arranged so as to be situated in the same zone of the substrate 2. Accordingly, the two security symbols 5, 6 are naturally superposed one on the other (although separated by the thickness of the substrate 2).

Here the substrate 2 is conformed to enable at the same time a examination by reflection of the two principle faces 3, 4 and at the same time examination by transmission of each of said faces. A substrate 2 such as that used in bills is appropriate, for example. The substrate 2 is for example paper or a polymer material.

At the level of the zone of the substrate 2 carrying the two security symbols 5, 6 the substrate 2 is preferably adapted to be more transparent than in the rest of the

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PCT/EP2017/081336 substrate 2 in order further to enhance examination by transmission. A zone may typically be rendered more transparent mechanically, by locally reducing the thickness of the substrate 2 (by a watermark technique, by rolling, etc.), or chemically, using a varnish, an ink or a solution either at the time of the formation of the substrate 2 or when the substrate 2 has been created.

The printing density of the inks may also be adapted to obtain a zone more transparent than the rest of the substrate 2.

Moreover, the printing density of the inks may be adapted so that one face of the document 7 is darker than the other. As a result, this enables observation with identical or quasi-identical rendering by reflection of the symbol carried by said lighter face and by transmission of the symbol carried by the darker face.

Here the security symbols 5, 6 are printed in inks other than those used for the rest of the substrate 2.

This makes it possible to facilitate observation of the various authentication marks.

The security symbols 5, 6 are typically printed in inks having a high contrast with respect to those used for the rest of the substrate 2 to facilitate examination by reflection, said inks moreover being relatively opaque to facilitate examination by transmission. Here the inks are inks visible in daylight.

As can be seen in figure 2, when the first principal face 3 is observed by reflection, the first authentication mark 7 formed by the first security symbol 5 is therefore clearly visible. For example, the first authentication mark 7 includes a scientific formula (E = MC²) and a drawing (a bolt of lightning).

As can be seen in figure 3, when the second principal face 4 is observed by reflection, the second authentication mark 8 formed by the second security symbol 6 is also

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PCT/EP2017/081336 clearly visible. For example, the second authentication mark 8 includes a word (Einstein).

On the other hand, if one of the two principal faces is observed by transmission (for example by looking at the first principal face 3), the two security symbols 5, 6 are visible by superposition of one on the other.

Because of their superposition, the two security symbols 5, 6 then trace out a third authentication mark 9 unrelated to the first authentication mark 7 and to the second authentication mark 8.

Note therefore that with two security symbols 5, 6 three authentication marks are created. Moreover, the third authentication mark 9 proves particularly difficult to reproduce because it exists only through the superposition of the two security symbols 5, 6 and therefore cannot be linked to any security symbol 5, 6 in isolation.

As can be seen in figure 4, here the third authentication mark 9 is a drawing (a diagram of electrons orbiting a nucleus).

The document 1 is therefore secured effectively and its fraudulent reproduction is very simple to detect by simple examination by transmission.

In fact, the security set is based on the following general principle.

An image M (hereinafter also referred to as a mask) is created here composed at random of black and white pixels, and therefore having no meaning. An image S (also termed a secret image) is moreover created the same size as the image M, also composed of black and white pixels, and representing something (a drawing, a geometrical figure, etc.) . An image C (also termed a cipher image) is then created using an exclusive-OR logic operator between the image M and the image S. The image C then has no meaning.

It then suffices to print the image C and the image M on different transparent sheets and then to superpose said

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PCT/EP2017/081336 sheets for a deciphered image D, corresponding to the image S but with less contrast, to appear at the level of the superposition of the images C and M. In fact, the superposition of the images C and M amounts to applying an OR logic operator between the image C and the image M, which therefore makes it possible for the image D to appear .

In the case of the present invention, the aim is nevertheless always to have authentication marks, that is to say images, having a meaning.

To this end, here the security set is produced in the following manner.

There are first chosen the three images II, 12, 13 that will in the end correspond to the first authentication mark 7, the second authentication mark 8 and the third authentication mark 9, respectively. Each of the three images II, 12, 13 therefore has a meaning but the three images II, 12, 13 are totally unrelated. The images II, 12, 13 are all of identical size, each pixel of each image being either black or white. The images II, 12, 13 therefore have a high contrast because there is a contrast of 100% between the black and white pixels of these images.

The images II, 12, 13 are then processed in the following manner.

Firstly, the first image II is broken down to form a mask Ml each pixel of which in reality forms a 2*2 matrix. As a result, the mask Ml is not the same size as the first image I1.

For a white pixel of the first image II, a pseudo white pixel is created in the mask Ml, that is to say a pixel the matrix of which comprises two white zones and two black zones. A pseudo white pixel in the mask Ml is therefore made up 50% of white zones. In order to create a mask, the black and white zones are distributed randomly in

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PCT/EP2017/081336 the pixel. A pseudo white pixel in the mask Ml is therefore chosen randomly from the following possibilities:

In the same way, for a black pixel of the first image II, a pseudo black pixel is created in the mask Ml, that is to say a pixel comprising one white zone and three black zones. A pseudo black pixel in the mask Ml therefore consists 75% of black zones. Similarly, the distribution of the black and white zones in the pixel is random. A pseudo black pixel in the mask Ml is therefore chosen randomly from the following possibilities:

EiBi

Because it is randomly constructed at the level of its pixels, a mark Ml is therefore obtained that nevertheless forms the first authentication mark 7, that is to say an image identifiable in itself, because the pixels of the matrix Ml are defined on the basis of the image II. In reality, the mask Ml forming the first authentication mark 7 (i.e. the scientific formula E = MC² and the bolt of lightning) is identical to the image II but has lower contrast than the image II because the white pixels of the mask Ml are formed 50% of white zones and the black pixels of the mask Ml are formed 75% of black zones.

The second image 12 is then broken down to form a cipher image C2 each pixel in which in reality forms a 2*2 matrix. The second image 12 and the cipher image C2 are therefore not the same size.

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In the same manner as for the mask Ml, a pseudo white pixel in the cipher image C2 is a pixel comprising two white zones and two black zones so that a pseudo white pixel in the cipher image C2 is composed 50% of white zones. As for a pseudo black pixel in the cipher image C2, this is a pixel comprising three black zones and one white zone i.e. a pixel composed 75% of black zones.

However, in contrast to the mask Ml, the distribution of the black and white zones in each pixel of the cipher image C2 is not chosen randomly.

In fact, the cipher image C2 must firstly correspond to the second image 12 in order to form the second authentication mark 8 (i.e. the word Einstein here) . As a result, if a pixel is black in the second image 12, the corresponding pixel of the cipher image C2 must also be a pseudo black pixel and if a pixel is white in the second image 12, the corresponding pixel in the cipher image C2 must also be a pseudo white pixel.

Moreover, the cipher image C2 must also be conformed so that the superposition of the mask Ml and the cipher image C2 forms the third authentication mark 9 linked to the third image 13.

Here the third authentication mark 9 corresponds to the deciphered image D3. The deciphered image D3 is such that each pixel in reality forms a 2*2 matrix. The third image 13 (which therefore corresponds to the secret image) and the deciphered image D3 are therefore not the same size. Moreover, a pseudo white pixel in the deciphered image D3 is a pixel comprising a white zone and three black zones so that a pseudo white pixel in the deciphered image D3 is composed 75% of black zones. As for a pseudo black pixel in the deciphered image D3, this is a pixel comprising four black zones i.e. a pixel composed 100% of black zones.

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Moreover, it must be remembered that the superposition of the mask Ml and of the cipher image C2 corresponds to the OR logic operator, that is to say:

for a superposed black pixel and white pixel of the mask Ml and of the cipher image C2 (or vice versa) the corresponding pixel of the deciphered image D3 will be black, for two superposed black pixels of the mask Ml and the cipher image C2 the corresponding pixel of the deciphered image D3 will be black, and for two superposed white pixels of the mask Ml and of the cipher image C2 the corresponding pixel of the deciphered image D3 will be white.

The cipher image C2 must therefore be constructed in accordance with the following rules:

yields C2 yields D3

- C2 OR Ml = D3

For example, for a black pixel of 13, a white pixel of 12 and a white pixel of Ml (linked to II), there are six possible combinations (12, 13, Ml) because Ml is chosen randomly and the pixels of 13 and of 12 are respectively 100% black and 100% white (the dimensions of the pixels shown not being respected hereinafter):

Ml

I I.·..¹

Remembering that there corresponds to a black pixel of 13 a pseudo black pixel of D3 composed 100% of black zones, we must furthermore have:

D3

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Moreover, given that the pixel of 12 concerned is white, the corresponding pixel of C2 must be pseudo white with the result that C2 can necessarily be chosen only from the following six possibilities:

EBBHSB

From then on, in order to comply with the aforementioned three rules, for each possible form of pixel of Ml there is only one possible form of pixel for C2 from 10 the six envisaged in order for the pixel of D3 to be 100% black as indicated above, namely:

According to another example, for a black pixel of 13, a black pixel of 12 and a white pixel of Ml (linked to II), there are six possible combinations (12, 13, Ml) because Ml

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PCT/EP2017/081336 is chosen randomly and the pixels of 13 and 12 are both 100% black (the dimensions of the pixels represented are not respected hereinafter):

Ml

E ]·ϋι

Remembering that a black pixel of 13 corresponds to a pseudo black pixel of D3 composed 100% of black zones, we must furthermore have:

D3

Moreover, given that the pixel of 12 concerned is black, the corresponding pixel of C2 must be pseudo black so that C2 can necessarily be chosen only from the following four possibilities:

EiBi

From then on, in order to comply with the aforementioned three rules, for each possible form of pixel of Ml there exist only two possible forms of pixel for C2 from the four that may be envisaged, namely:

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If Ml =	Then C2 =
E	a o - L·
3	a o L·
B	L· o - B
S	B o L·
	L· o 9
S	a o - r

In this case, the form of the pixel of C2 is chosen randomly from the two possible ones.

For all possible combinations (12, 13, Ml), there therefore exist one or more possible forms of pixel for C2 that make it possible to comply with the aforementioned three rules.

The cipher image C2 that forms the second authentication mark is therefore constructed, that is to say an image identifiable in itself because the pixels of the cipher image C2 are defined on the basis of the image 12. In reality, the cipher image C2 forming the second authentication mark is identical to the image 12 but has lower contrast than the image 12 because the pseudo white pixels of the cipher image C2 are formed 50% of white zones and the pseudo black pixels of the encrypted image C2 are formed 75% of black zones.

As a result, it remains only to print a cipher image C2 and the mask Ml on respective faces of the substrate 2

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2017367204 28 May 2019 to form the first authentication mark 7 and the second authentication mark 8, respectively.

In use, and superposing the two authentication marks 7, 8 (i.e. the cipher image C2 and the mask Ml), that is to 5 say by looking at them by transmission, the deciphered image D3 is therefore obtained. In reality, the deciphered image D3, which is also the third authentication mark 9, is identical to the image 13 but has lower contrast than the image 13 because the white pixels of the deciphered image 10 D3 are formed 25% of white zones and the black pixels of the deciphered image D3 are formed 100% of black zones.

Note that the images represented in the various figures of the present application are diagrammatic because (for reasons of visibility) they do not show the lower 15 contrast of the mask Ml and of the cipher image C2 relative to the initial images, or again the lower contrast of the deciphered image D3 with the corresponding initial image on the one hand or with the mask Ml and the cipher image C2 on the other hand. 20 A second embodiment of the invention is described next with reference to figure 5.

Here the second embodiment is identical to the first embodiment except that the security set includes a third security symbol 110 arranged in the interior of the 25 substrate 102.

In particular, the substrate 102 is formed so that the third security symbol 110 is arranged in the same zone of the substrate 102 as the other two security symbols 105,

106. The three security symbols 105, 106, 110 are therefore 30 naturally superposed (but not juxtaposed because of the thickness of the substrate). Alternatively, the symbols are arranged so that at least two of the three symbols are juxtaposed (for example by production of two separate films each carrying a security symbol and subsequent 35 juxtaposition of said films).

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Here the third security symbol 110 is conformed to form by reflection a fourth authentication mark 111 (for example an apple) unrelated to the first authentication mark 107, the second authentication mark 108 and the third authentication mark 109 that is formed by the superposition of the first security symbol 105 and the second security symbol 106 alone (respectively the formula E = MC² plus the bolt of lightning, the set of electrons and the nucleus and a symbol FAUX (FALSE)). When the first principal face 103 is observed by reflection, the first authentication mark 107 formed by the first security symbol 105 is therefore clearly visible.

If the second principal face 104 is observed by reflection, the second authentication mark 108 formed by the second security symbol 106 is also clearly visible.

On the other hand, if one of the two principal faces is observed by transmission (for example by looking at the first principal face 103), the three security symbols 105,

106, 110 can be seen superposed. Because of their superposition, the three security symbols 105, 106, 110 then trace out a fifth authentication mark 112 (here a star) unrelated to the first authentication mark 107, the second authentication mark 108, the third authentication mark 109 and the fourth authentication mark 111.

Note that with three security symbols 105, 106, 110 five authentication marks are therefore created. Moreover, the fifth authentication mark 112 proves particularly difficult to reproduce because it exists only through the superposition of the three security symbols and therefore cannot be linked to any security symbol in isolation.

In this embodiment, the mask/cipher image/deciphered image principle is applied to the first authentication mark

107, to the second authentication mark 108 and to the fifth authentication mark 112 but by means of three security symbols 105, 106, 110.

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If a person attempts to copy the document by scanning it, they will advantageously scan both faces of the bill and therefore scan the authentication marks 107, 108 but without being able to scan the inaccessible fourth authentication mark 111. As a result, once the fraudulent document has been created, when looking by transmission at the level of the reproduction of the authentication marks 107, 108 the symbol FAUX will appear indicating that the bill has been reproduced fraudulently.

A document 101 of this kind therefore proves to be particularly well protected.

The three security symbols 105, 106, 110 are optionally printed in inks having at least one absorption/excitation wavelength common to the three security symbols. The third security symbol 111 is moreover printed in inks also having at least one absorption/excitation wavelength different from those of the other two security symbols.

For example, the three security symbols 105, 106, 110 are all visible in daylight and the third security symbol 110 is moreover the only one visible in infrared light.

As a result, depending on the illumination, it is possible to view in turn the various authentication marks, which makes the document 101 particularly well secured.

Numerous variants may be envisaged here.

Thus the third authentication mark 109 need not exist. The superposition of the first authentication mark 107 and of the second authentication mark 108 then yields no authentication mark (whether it can be interpreted or not). This is not a problem for obtaining the fifth authentication mark 112, however.

Alternatively, the third security symbol 110 is conformed so that the fourth authentication mark 111 is related to the third authentication mark 109 by the

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PCT/EP2017/081336 superposition of the first security symbol 105 and of the second security symbol 106.

A third embodiment of the invention is described next with reference to figure 6.

Here the third embodiment is identical to the second embodiment except that the fourth authentication mark 213 cannot be interpreted, being in no way a figurative symbol. Moreover, the first security symbol 205 and the second security symbol 206 are also conformed so that the superposition of these two security symbols 205, 206 alone does not form a third authentication mark that can be interpreted. Like the third security symbol 210, the superposition of the first security symbol 205 and the second security symbol 206 therefore forms a third authentication mark 214 that cannot be interpreted, with no figurative symbol (for reasons of visibility the authentication marks 213 and 214 are represented by a white square but are in reality formed by a cloud of points forming a zone more opaque than that shown).

On the other hand the three security symbols 205, 206, 210 are always conformed so as conjointly to form by superposition a fifth authentication mark 212 unrelated to the first authentication mark 207, the second authentication mark 208, the fourth authentication mark 213 and here the third authentication mark 214.

When the first principal face 203 is observed by reflection the first authentication mark 207 formed by the first security symbol 205 is therefore clearly visible (here the formula E = MC² and the bolt of lightning).

When the second principal face 204 is observed by reflection the second authentication mark 208 formed by the second security symbol 206 is also clearly visible (here the electrons orbiting around the nucleus).

On the other hand, when one of the two principal faces is observed by transmission (for example by looking at the

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PCT/EP2017/081336 first principal face 203), the three superposed security symbols 205, 206, 210 can be seen. Because of their superposition, the three security symbols 205, 206, 210 then trace out the fifth authentication mark 212 (here a star) neither related to the first authentication mark 207, the second authentication mark 208, the fourth authentication mark 213 nor related to the third authentication mark 214.

In this embodiment, the mask/cipher image/deciphered image principle is applied to the first authentication mark 207, to the second authentication mark 208 and to the fifth authentication mark 212 but by means of three security symbols 205, 206, 210.

This makes it possible to make fraudulent reproduction of the document 201 even more complicated.

Note therefore that with three security symbols 205, 206, 210 five authentication marks are created. Moreover, the fifth authentication mark 212 proves particularly difficult to reproduce because it exists only through the superposition of the three security symbols 205, 206, 210 and therefore cannot be linked to any security symbol 205, 206, 210 in isolation.

Alternatively, only the third security symbol 210 or only the superposition of the first security symbol 205 and the second security symbol 206 will not form an authentication mark that can be interpreted.

Alternatively, the third authentication mark 214 need not exist. The superposition of the first authentication mark 207 and of the second authentication mark 208 then yields no authentication mark (whether it can be interpreted or not) . This is not a problem for obtaining the fifth authentication mark 212, however.

A fourth embodiment is described next with reference to figure 7. This embodiment is identical to the first embodiment except that the second security symbol 308 is

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PCT/EP2017/081336 arranged in a window 315 provided in the substrate 302 so that the second security symbol 308 is visible on both faces of the substrate 302 by reflection. The window 315 is arranged in a zone of the substrate 302 other than that where the first security symbol 305 is situated.

When the first principal face is observed by reflection, the first authentication mark 307 formed by the first security symbol 305 is therefore clearly visible (here the symbol @) . Moreover, the second authentication mark 308 formed by the second security symbol 306 can also be seen (here a gear).

When the second principal face is observed by reflection, the second authentication mark 308 formed by the second security symbol 306 can also be seen because of the window 315. The first authentication mark 307 is not visible by reflection, however.

If the substrate 302 is now folded so as to place the window 315 against the first security symbol 305, the two security symbols 305, 306 are then superposed and the third authentication mark 309 (here the letter A) can then be observed by reflection.

Alternatively, the various security symbols may also be defined so that if the substrate 302 is folded, this time to place the first security symbol 305 on the window 315, a fourth authentication mark different from the third authentication mark can then be seen at the level of the superposition of the two security symbols.

Note that with two security symbols 305, 306 at least three authentication marks are therefore created. Moreover, the third authentication mark 309 (and where applicable the fourth authentication mark) prove (s) particularly difficult to reproduce because it exists only through the superposition of the two security symbols 305, 306 and therefore cannot be linked to either security symbol 305, 306 in isolation.

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Instead or in addition, there may be a different number of security symbols printed on the first face of the document 301 on which the security symbol 306 carried by the window 315 may be superposed to form other authentication marks and/or there may be different windows each carrying a security symbol for forming other authentication marks when the window 315 is placed over the first security symbol 305 or other security symbols formed on the first face of the document 301. A fifth embodiment is described next with reference to figure 8.

Whereas in the other embodiments the set of security symbols was carried by the same document, in the fifth embodiment the first security symbol 405 is always carried by the document 401 but the second security symbol 406 is displayed on the screen 417 of a device 416. Here the device 416 is a mobile telephone.

When the first principal face of the document 401 is observed by reflection, the first authentication mark 407 formed by the first security symbol 405 is therefore clearly visible (here the symbol €).

If the screen 417 is observed, the second authentication mark 408 formed by the second security symbol 406 can also be seen (here a star).

If the document 401 is now placed against the screen 416 so as to superpose the first security symbol 405 and the second security symbol 406, the two security symbols 405, 406 are then superposed and the third authentication mark (not shown here) can then be observed.

To simplify the task of the user, the device 416 preferably forms part of a superposition device comprising a video camera 421 connected to the device 416 to measure the relative position of the document 401 on the screen 417. On the basis of data supplied by the video camera 421, the device 416 automatically repositions the second

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PCT/EP2017/081336 security symbol 406 so that it is arranged under the first security symbol 405.

The video camera 421 is preferably integrated into the device 416. The video camera 421 is therefore the video camera of the mobile telephone.

In order to facilitate the task of the video camera 421 the device includes a system 418 for identifying the position of the document 401 of the screen 417. Here the identification system includes a plate 419 arranged on the device 416. The plate 419 includes for example means for clipping it to the device 416 so as to be easily removable. Here the plate 419 is arranged at the end of the device 416 at the level of the video camera 421, the plate 419 extending substantially perpendicularly to the device 416.

The plate 419 moreover includes a mirror 420 arranged at the top end of the plate 419 so as to overlie the video camera 421. The mirror 420 is such that the measurement field of the video camera 421 (centered on an aiming direction A) passes through said mirror 420 and is moreover adapted to reflect the screen 417 of the device 416 in the measurement field of the video camera. As a result the video camera 421 is able to view the screen 417 via the mirror 420. On the basis of the images reflected onto the mirror 420, the video camera 421 transmits the corresponding images of the position of the document 401 on the screen 417 to the device 416, which enables the device 416 to determine the relative position of the first security symbol 405 and to position the second security symbol 406 accordingly.

Here the mirror 420 is arranged to reflect the entirety of the surface of the screen 417 in the measurement field of the video camera.

Three authentication marks are therefore created using two security symbols 405, 406. Moreover, the third authentication mark proves particularly difficult to

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PCT/EP2017/081336 reproduce because its exists only through the superposition of the two security symbols 405, 406 and therefore cannot be linked to any security symbol 405, 406 in isolation.

A sixth embodiment of the invention is described next with reference to figures 9a to 9c. It has already been seen in the previous embodiments that the third authentication mark could be detected by superposition of the two security symbols in numerous different ways, for example by inspection by transmission, by folding, etc. Any other means of revealing the third authentication mark may be envisaged in the context of the present invention.

Accordingly, in this sixth particular embodiment of the invention the security set is conformed so that the various authentication marks can be examined only by reflection and without bending the object 501 carrying the security set.

To this end, the two security symbols are printed directly one on top of the other using inks having at the same time at least one common absorption/excitation wavelength and at the same time at least one absorption/excitation wavelength different from that of the other ink. As a result, the third authentication mark is revealed when the set of two security symbols is illuminated using their common absorption/excitation wavelength.

For example, the first security symbol is printed using an ink visible in daylight and under infrared excitation using a wavelength around 800 nanometers. The second security symbol is printed using an ink visible in daylight and under infrared excitation using a wavelength around 900 nanometers. The two symbols are printed one on top of the other directly on the object 501 or on an element attached to the object 501. The two symbols are therefore arranged in the same zone of the object 501.

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Referring to figure 9b, if the object 501 is illuminated with infrared light centered on the wavelength of 800 nanometers only the first security symbol will react so as to cause the first authentication mark 507 (here a cross surrounded by the circle) to appear, which mark is then visible by reflection.

Referring to figure 9c, if the object 501 is illuminated under infrared light centered on the wavelength 900 nanometers only the second security symbol will react so as to cause the second authentication mark 508 (here a star) to appear, which mark is then visible by reflection.

Finally, referring to figure 9a, if the object 501 is illuminated in the visible spectrum, the two security symbols will react so as to cause the third authentication mark 509 (here a heart) to appear through superposition of the two security symbols, which mark is therefore also visible by reflection).

In this embodiment, depending on the illumination with which the object 501 is examined by reflection, the first authentication mark 507, the second authentication mark 508 or the third authentication mark 509 appears.

Note that with two security symbols three authentication marks are therefore created. Moreover, the third authentication mark 509 proves particularly difficult to reproduce because it exists only through the superposition of the two security symbols and therefore cannot be linked to any security symbol in isolation.

Alternatively, other types of inks could of course be used and thus visible spectrum/ultraviolet or visible spectrum/ultraviolet/infrared inks .

The invention is not limited to what has just been described and to the contrary encompasses any variant within the scope defined by the claims.

Although here the set according to the invention is carried by the same document or by a document and a device

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PCT/EP2017/081336 having a screen, this is not limiting on the invention and the set according to the invention could be carried in any other manner. For example, the set according to the invention could be carried in whole or in part by an object other than a document such as for example a token or a coin. The set according to the invention could be carried in part by a first object and in part by another, second object mounted on the first to cause at least one third authentication mark to appear. The second object is a polarizing filter for example.

In particular, although here the security symbols are printed directly on the substrate carrying them, the security symbols could be formed directly on a dedicated base itself mounted on the support afterwards.

For example, the base could be a filament carrying at least one of the security symbols, the security symbol being inserted on the base before or after arranging the base on the substrate. One or more security symbols will then be arranged in the substrate instead of being on one of the principal faces of the substrate like that which has been described. The security symbol will for example be inserted in the substrate at the level of a window formed in the substrate so that the filament is accessible from both sides of the substrate. The filament will then be conformed to enable inspection by reflection and/or inspection by transmission of said filament. The filament could typically be a multilayer film with interference effects such as that described in the present applicant's patent application FR 3 011 508.

Alternatively, the substrate could be a patch, a film such as a polymer film, etc. carrying at least one of the security symbols, the security symbol being inserted on the substrate before or after arranging the base on the substrate .

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The base could cover or fill a hole formed in the substrate in order to form a window so that the security symbol is then accessible from both sides of the substrate. The base will then preferably, although not exclusively, be conformed to enable inspection by reflection and/or transmission of said symbol.

Of course at least one of the security symbols could be arranged in one way on the substrate and at least one other security symbol could be arranged in another way on the substrate: there could then be a security symbol arranged on a filament and a security symbol arranged on a patch.

Moreover, although the inks used here are inks visible in daylight, the inks used could instead or additionally be inks visible using other, typically infrared or ultraviolet, wavelengths. The inks being visible in daylight will be preferred when it is wished that a user lambda be able to detect counterfeiting easily or to the contrary that the inks are invisible in daylight to complicate fraudulent reproduction of the security set.

The inks could be invisible in daylight and visible under ultraviolet or infrared excitation. The inks could be visible in daylight and fluorescent under ultraviolet or infrared excitation. Inks could equally be used re-emitting different colors on a first face of the substrate and on the second face of the substrate: as a result when two security symbols are superposed the third authentication mark will appear in a panel of colors comprising the first color of the first authentication mark, the second color of the second authentication mark and in a third color resulting from the combination of said two colors to further complicate fraudulent reproduction of the set of the invention.

Although here the security symbols are printed, the security symbols could be formed differently on the

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PCT/EP2017/081336 substrate or on a base mounted on the substrate, for example by embossing, by metallization, by demetallization, etc .

Different techniques could obviously be combined to create the same security symbol and/or to create two different security symbols.

Although the authentication marks cited here are figures, drawings, words, mathematical formulas, etc., the authentication marks could be different. At least one of the authentication marks could therefore comprise an authentication code of the substrate or of the object carrying it such as for example a one-dimensional barcode, a two-dimensional barcode, a serial number, a Sealgn@ture (registered trademark) code, etc. At least the authentication mark revealed by superposition of the various security symbols will preferably comprise an authentication code of this kind.

Although here it has been indicated that the security set was fabricated from images broken down into mask/cipher image/deciphered image the pixels of which were 2*2 matrices, it is understood that said matrices could be of different size, for example 2*3 or 3*2, in particular although not exclusively to create different levels of contrast or to enable superposition of a greater number of security symbols. The matrices could equally have shapes other than square or rectangular and for example be of circular or hexagonal shape to increase the difficultly of fraudulent reproduction.

Although here the terms black and white are used to refer to the various pixels, this is not limiting on the invention and there could be matrices constituting the various images, masks, etc. composed of pixels of other colors .

Although here the authentication marks are visible to and can be inspected by the naked eye, it could be

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PCT/EP2017/081336 otherwise. Ultraviolet or infrared illumination could therefore be required to examine at least one authentication mark, or a (linear or circular) polarizing filter .

When one of the security symbols is carried by an object and the other security symbol is displayed on a device including a screen, the device including a screen could include and/or be associated with sensors other than a video camera for estimating the position of the object on the screen. For example, where the screen is touchsensitive, it could be the touch-sensitive detectors on the screen that enable direct determination of the relative position of the object on the screen.

The device could be other than a mobile telephone. The device could for example be a computer, a touch-sensitive tablet computer, and generally speaking any device including a screen.

Although here the sensor is integrated into the device, the sensor could be external to and remote from the device. The sensor would then be connected to the device by cables (for example by USB cables) or wirelessly (for example by Bluetooth).

An identification system could be dispensed with for example by equipping the device with one or more stops so that the user is able to position the object in a predetermined manner.

The identification system could include a different number of mirrors. Instead or additionally the identification system could include optical elements other than a mirror such as one or more optical fibers, one or more lenses, etc.

The screen could be used to improve the contrast of the third authentication mark and/or of the second security symbol.

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Although here the second security symbol displayed on the screen is fixed, there could instead be a second security symbol that is modified regularly on the screen so that with a first security symbol placed on it the third 5 authentication mark also changes regularly (each time the second security symbol is modified). There could therefore be evolution, movement of the third authentication mark.

The device could be used to authenticate an object, the detection of counterfeiting then coming directly from 10 the device thanks to the possible observation of the third authentication mark by the video camera of the device or could be left for the user to assess through viewing the effects produced.

Claims

1. A set of N security symbols (5,6; 105,106,110; 205,206,210; 305,306; 405,406), each security symbol forming on its own an authentication mark different from those formed by the other security symbols, the various security symbols being conformed to form conjointly by superposition of the N security symbols an N+l^thauthentication mark (9; 112; 212; 309; 509) unrelated to the other N authentication marks each formed by a respective one of the N security symbols.

2. The set as claimed in claim 1, in which at least two security symbols are carried by the same object (5, 6; 105, 106, 110; 205, 206, 210; 305,306).

3. The set as claimed in claim 2, in which at least one of the security symbols (5,6; 105,106; 205,206) is arranged on the first principal face of the object and at least one other security symbol is arranged on the second principal face of the object, the two symbols being arranged in the same portion of the object.

4. The set as claimed in claim 2 or claim 3, in which at least two of the security symbols (305, 306) are arranged on the same principal face of the object, folding

of the obj ect enabling superposition of the two security symbols • 5. The set as claimed in any one of the preceding claims, in whi ch N is at least equal to 3. 6. The set as claimed in claim 5, in which the at

least three security symbols are printed using inks having at least one absorption/excitation wavelength common to the three security symbols, the third security symbol furthermore being in an ink having at least one absorption/excitation wavelength that is specific to it and to which the other two security symbols do not react.

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7. The set as claimed in any one of the preceding claims, in which at least one of the security symbols (406) is displayed on a device (416) including a screen (417) and at least one other security symbol (405) is carried by an object (4 01) .

8. The set as claimed in any one of the preceding claims, in which at least one of the security symbols carried by an object is in an ink different from those of the rest of the object.

9. The set as claimed in any one of the preceding claims, in which at least one of the security symbols (5,6; 105, 106, 110; 205, 206, 210; 305,306; 405) is in an ink visible in daylight.

10. The set as claimed in any one of the preceding claims, in which at least a first security symbol is printed using an ink having a first absorption/excitation wavelength and a second absorption/excitation wavelength and at least one second security symbol is printed over the at least one first security symbol in an ink having the first absorption/excitation wavelength and a third absorption/excitation wavelength different from the second absorption/excitation wavelength.

11. The set as claimed in any one of the preceding claims, in which the at least one first security symbol and the at least one second security symbol are printed using inks that re-emit different colors in order for the third authentication mark to appear in a panel of colors comprising a color resulting from the combination of said colors of the at least one first security symbol and of the at least one second security symbol.