EP4026085A1

EP4026085A1 - Method for inserting information into an image and corresponding device

Info

Publication number: EP4026085A1
Application number: EP20761865.3A
Authority: EP
Inventors: Gaëtan LE GUELVOUIT; Valérie DENIS
Original assignee: Fondation B Com
Current assignee: Fondation B Com
Priority date: 2019-09-06
Filing date: 2020-09-02
Publication date: 2022-07-13
Also published as: FR3100648A1; FR3100648B1; US20220292624A1; WO2021043817A1

Abstract

A method for inserting information into a first image comprising N1 rows x M1 columns of elements comprises the following steps: a) obtaining (E21), from the first image, a second image comprising N0 rows x M0 columns of elements, with N0≤N1 and M0≤M1, b) generating (E22), from the second image, initial information comprising N0 rows x M0 columns of elements, c) obtaining, from the generated initial information, intermediate information comprising N4 rows x M4 columns of elements, such that N4≥N1 and M4≥M1 on the one hand, and N4=kx.N0 and M4=ky.M0 on the other hand, kx and ky being integers greater than or equal to 1, the elements of the intermediate information being organised into blocks, d) obtaining (E23) the information to be inserted from the intermediate information, comprising, for at least one block of intermediate information: - generating a sequence of symbols representative of a noise, comprising as many symbols as there are elements included in the block, at least one of the symbols not being zero, such that the result of a predetermined function applied to the symbols is equal to a chosen value, - adding each symbol to the corresponding element of the block, and e) inserting (E24) the obtained information into the first image.

Description

Method of inserting information into an image and corresponding device

Technical field of the invention

The present invention relates generally to the technical field of digital watermarking of an image or of a video sequence.

It relates in particular to a method and device for inserting information (also called watermark or identification mark) into an image. One aim of this technique is, for example, to identify the author of the tattooed image, thanks to the information inserted.

State of the art

It has been proposed to insert into an image or images of a video sequence, a digital watermark, that is to say imperceptible and therefore undetectable information, identifying the image or video in question. This information must be able to be found despite the transformations that the image in which it has been inserted may undergo. Different techniques exist. These are all expressed in the form of a function translating the addition of a watermark W to an image I such that IW = I + W, IW being the watermarked image (see IJ Cox, ML Miller and JA Bloom, Digital watermarking, Sec. 3.3, Communication-based models of watermarking, p. 68, Morgan Kaufman Publishers.)

In order for the tattoo to be robust to scaling like an enlargement, it is known to calculate the information to be inserted in a fixed and reduced dimension, then to enlarge it to the size of the image to be tattooed. This technique is for example described in the manual: I. J. Cox, M. L. Miller and J. A. Bloom, Digital watermarking, Sec. 9.1.6, Preinverting distortions in the embedder, p. 304, Morgan Kaufman Publishers.

However, the magnification step of this solution generates uniform solid areas in the watermarked image, once the watermark is inserted, regardless of the magnification method used. These areas (in particular the luminosity transitions between two adjacent solid areas) are easily visible, which makes the watermark detectable.

Presentation of the invention

In this context, the invention proposes a method of inserting information in a first image comprising N1 rows x M1 columns of elements, N1 and M1 being non-harmful integers, said method comprising the following steps: a) obtaining from the first image, a second image comprising NO rows x MO columns of elements, N0 and MO being non-zero integers such as N0 £ N1 and M0 £ M1, b) a generation, from the second image, initial information comprising NO lines x MO columns of elements, c) obtaining from the generated initial information, intermediate information comprising N4 lines x M4 columns of elements, so that N4³N1 and M4³M1 on the one hand, and N4 = kx.N0 and M4 = ky.M0 on the other hand, N4 and M4 being undamaged integers, kx and ky being integers greater than or equal to 1, said elements of the intermediate information being organized in blocks, d) obtaining said information to be inserted from the intermediate information, comprising at least one block of the intermediate information,

a generation of a sequence of symbols representative of a noise, comprising as many symbols as there are elements included in said block, at least one of the symbols being non-zero, so that the result of a predetermined function applied to said symbols is equal to a chosen value,

- an addition of each symbol to the corresponding element of said block, and e) an insertion of said information obtained in the first image.

The invention has the advantage of allowing the insertion of information that is robust to the change in scale of the image without which it was inserted, and that does not generate a solid in the watermarked image.

For example, the result can be a sum.

The predetermined function may be a measure of central tendency.

For example, the predetermined function can be is the median.

For example, the predetermined function can be the average.

Alternatively, the predetermined function (applied to the symbols) may be the sum (of the symbols).

The intermediate information is, for example, obtained from the initial information by means of a magnification method (for example by means of a method of interpolation to the nearest neighbor).

According to one embodiment, said chosen value is equal to zero; moreover, provision can be made, for example, for kx or ky to be greater than or equal to 2. According to one embodiment, if N4> N1 or if M4> M1, obtaining the information to be inserted further comprises, following the addition of each symbol to the corresponding element of said block, a reduction of the size of the intermediate information so as to obtain respectively N4 = N1 or M4 = M1.

According to one embodiment, said sequence of symbols representative of the noise comprises p symbols, such that p1 symbols are generated randomly or pseudo-randomly and p2 symbols are calculated so that the result of the predetermined function applied to the p symbols, namely equal to said chosen value, p, p1 and p2 being integers such that p = p1 + p2.

The invention also proposes, according to another aspect, a method of extracting information formed from a plurality of elements comprising N0 rows and MO columns, inserted into an image comprising N2 rows x M2 columns of elements using the insertion method according to one of the embodiments described above, N0, MO, N2 and M2 being non-harmful integers, such as N2> N0 and M2> M0, said insertion method comprising the steps following: f) obtaining from said image, a new image comprising N3 rows and M3 columns of elements, with N3³N2 and M3³M2 on the one hand, and N3 = nx.N0 and M3 = ny.M0 d ' on the other hand, N3 and M3 being positive undamaged integers, nx and ny being integers greater than 1, the elements of said new image being organized in blocks, g) obtaining a reduced image from the new image, the reduced image comprising N0 rows x MO columns of elements, each element of the reduced image being obtained from the elements of a block c corresponding in the new image, and for each element of the reduced image to be obtained:

a determination of the value of the element considered by applying said predetermined function to the values of the elements of the block of the new image corresponding to said element, the value of said element considered corresponding to the result of the application of the function, and h) a extracting information from the reduced image.

The invention also proposes, according to another aspect, a device for inserting information into a first image comprising N1 lines x M1 columns of elements, N1 and M1 being non-harmful integers, the device being configured to put in implements the following steps: i) obtaining from the first image, a second image comprising NO rows x MO columns of elements, N0 and MO being non-zero integers such as N0 £ N1 and M0 £ M1, j) generation, from the second image, initial information comprising NO lines x MO columns of elements, k) obtaining from the generated initial information, intermediate information comprising N4 lines x M4 columns of elements, so that N4³N1 and M4³M1 on the one hand, and N4 = kx.N0 and M4 = ky.M0 on the other hand, N4 and M4 being undamaged integers, kx and ky being integers greater than or equal to 1, said elements of the intermediate information being organized in blocks,

L) obtaining said information to be inserted from the intermediate information, comprising at least one block of the intermediate information

- an addition of each symbol to the corresponding element of said block, and m) an insertion of said information obtained in the first image.

The invention also proposes, according to another aspect, a device for extracting information formed from a plurality of elements comprising N0 rows and MO columns, inserted into an image comprising N2 rows x M2 columns of elements using of the insertion method according to one of claims 1 to 7, N0, MO, N2 and M2 being undamaged integers, such as N2> N0 and M2> M0, the device being configured to implement the following steps: n) obtaining from said image, a new image comprising N3 rows and M3 columns of elements, with N3³N2 and M3³M2 on the one hand, and N3 = nx.N0 and M3 = ny.M0 on the other hand , N3 and M3 being positive undamaged integers, nx and ny being integers greater than 1, the elements of said new image being organized in blocks, o) obtaining a reduced image from the new image, l ' reduced image comprising N0 rows x MO columns of elements, each element of the reduced image being obtained from the elements of a block c corresponding in the new image, and for each element of the reduced image to be obtained: a determination of the value of the element considered by applying said predetermined function to the values of the elements of the block of the new image corresponding to said element, the value of said element considered corresponding to the result of the application of the function, and p) a extracting information from the reduced image.

The invention also provides, according to another aspect, a recording medium readable by a computer, on which is recorded a computer program comprising program code instructions for the execution of the steps of the method as described above. .

Of course, the different characteristics, variants and embodiments of the invention can be associated with each other in various combinations insofar as they are not incompatible or mutually exclusive.

Detailed description of the invention

In addition, various other characteristics of the invention emerge from the appended description given with reference to the drawings which illustrate non-limiting embodiments of the invention and in which:

- Figure 1 illustrates an example of application of an embodiment of the information insertion and extraction methods according to the invention;

- Figure 2 shows an embodiment of an insertion method according to the invention;

- Figure 3 illustrates the embodiment of Figure 2;

- Figure 4 shows in more detail a step of the embodiment of Figure 2;

- Figure 5 illustrates an element implemented in the step shown in Figure 4;

- Figure 6 illustrates a block implemented in the step shown in the figure

4;

- Figure 7 illustrates the block of Figure 6, after adding noise;

- Figure 8 shows an example of rendering of information to be inserted;

- Figure 9 shows an embodiment of an extraction process according to the invention; and

- Figure 10 shows an embodiment of a device according to the invention. FIG. 1 describes an example of application of an embodiment of the methods of inserting and extracting information according to the invention. A first step E10 implements a method of inserting information into an image. This information can for example be a mark making it possible to recognize the author of the image for the purposes of protecting the image by copyright. As a variant, the information (hereinafter called “watermark”) can be inserted into one or more images of a video sequence.

Once the information has been inserted into the image, the latter can be transmitted during a step E11 and then received by a client at step E12. The image can then be transformed by the customer, who can for example operate a change of scale, step E13.

The information that was inserted in step E10 is extracted from the transformed image, step E14, then analyzed, for example to identify the author of the image, step E15.

FIG. 2 illustrates in more detail an example of the implementation of the method of inserting information into an image, step E10.

We consider an image l (D1) formed of several elements, for example pixels, distributed in N1 lines and in M1 columns, N1 and M1 being undamaged integers representing the dimensions D1 of the image l (D1). These dimensions can be expressed as an N1 x M1 pixel product. For example, the dimensions D1 can be equal to 3840 × 2160 pixels.

From this image, we obtain another image l (D0) formed of elements distributed in N0 rows and MO columns, N0 and MO being non-harmful integers representing the dimensions D0 of the image l (D0). It comes N0 £ N1 and / or M0 £ M1, corresponding to the 16: 9 aspect ratio.

The dimensions D0 are predetermined, for example equal to 640 × 360 pixels, corresponding to the so-called 360p definition. Preferably, the dimensions D0 are chosen so that the ratio between the number of rows and columns corresponds to a standard image format such as the 16/9 image format. For example, these dimensions D0 can imply a number of pixels corresponding to a standard definition SD, ie 480p. More generally, in the context of the invention described below, the dimensions D0 are chosen sufficiently small so that the watermark remains robust to image reductions in formats of acceptable quality from the viewpoint of a viewer, and large enough that the energy of the watermark remains low compared to the energy of the host image. It will be recalled that conventionally, in the field of signal processing, the energy of an image corresponds to the variance of the values of the pixels with respect to a constant value.

From this image I (D0), a watermark W (D0) (or initial information) is generated, step E22. The watermark W (D0) is also formed of pixels distributed in rows and columns. Methods of calculating a tattoo at a given size from an image having this same size are known to those skilled in the art. Calculation methods are described for example in the Digital watermarking manual mentioned above. It is this initial information that will subsequently be extracted for analysis.

From this watermark W (D0), an enlarged watermark W (D4) is obtained so as to have N4 rows and M4 columns (dimensions D4), step 23, according to an embodiment of the method of the invention. There comes N4³N1 and M4³M1 on the one hand, and N4 = kx.N0 and M4 = ky.M0 on the other hand, N4 and M4 being undesirable integers, kx and ky being integers greater than or equal to 1. This step 23 is described in more detail below.

Preferably, the dimensions N4 and M4 are slightly greater than N1 and M1. For example, if N1 = rx.N0 and M1 = ry.M0 (rx and ry being numbers greater than 1), we can choose N4 and M4 such that N4 = (E (rx) +1) .N0 and M4 = (E (ry) +1) .M0, E (.) Corresponding to the function “whole part”. For example if D1 = 3840 ^* 2160 pixels, we can have D4 = 4480 ^* 2520 pixels.

If N4> N1 or M4> M1, step 23 further comprises a reduction of the dimensions D4 of the watermark W (D4) so that N4 = N1 and M4 = M1.

Finally, the enlarged watermark W (D4) is inserted into the image 1 (D1), step 24, so as to obtain the watermarked image IW (D1). The insertion of the enlarged watermark W (D4) in the image l (D1) is done for example by addition, that is to say by adding the values of the pixels of the watermark W (D4) to the values of the corresponding pixels in image l (D1). The enlarged tattoo once inserted is therefore superimposed on the image.

The image l (D1) can be a still image or one of the images of a video sequence, several images (or even all of the images) of the video sequence being able to be watermarked.

Alternatively, the image can be a color component, such as luminance or a chrominance component. Each color component is made up of elements, one element corresponding to the color component of a pixel. FIG. 3 schematically illustrates the changes in dimensions implemented during the various stages. For this figure, it is considered, for the sake of simplification, that the first image 1 (D1) is formed of 4 ^* 4 pixels. In step E21, the second image l (D0) at the second dimension D0, the value of which is equal to 2 ^* 2 pixels, is obtained from the first image l (D1).

The watermark W (D0) formed of 2 ^* 2 pixels is generated from this image I (D0), step E22. Then the tattoo is enlarged to the dimensions D4. If N4> N1 or M4> M1, step 23 further comprises, as illustrated in FIG. 3, a reduction in the dimensions so as to have N4 = N1 and M4 = M1.

Finally, the watermark W (D1) is inserted in the image l (D1). We then obtain the watermarked image IW (D1) formed of 4 ^* 4 pixels, step 24.

FIG. 4 illustrates in more detail the step of resizing the watermark, E23. The resizing is done in two stages. We consider an element having the value v belonging to the watermark in the second dimension W (D0, v), as illustrated in FIG. 5. Using a known magnification method for example the so-called Closest Neighbor interpolation method or PPV (in English: “Nearest Neighbor interpolation”), with an integer enlargement factor sx for the rows and sy the columns, we obtain a block V of sx ^* sy elements v, at step E230. For example, for the sake of simplification, we consider here a magnification factor such that sx = sy = 3, so that the resulting block comprises 3 ^* 3 elements, that is to say nine elements in all as illustrated in FIG. 6. obtains the enlarged watermark W (D4, V) (intermediate information).

Then for at least one block V of the enlarged watermark, a noise b is then generated with as many symbols b [i] as there are elements in the block V (i being an integer such as 1 <i £ (sx ^* sy)) . At least one of these symbols b [i] is different from zero. The noise and in particular the distribution of the noise, is generated so that the result of a predetermined function applied to the symbols b [i] is equal to the same value chosen for the block considered, whatever the values taken by these symbols. bi].

In the example described, the predetermined function is a measure of central tendency (applied to the symbols b [i]), here the average of the symbols b [i] or, alternatively, the median of the symbols b [i].

For example, the values taken by the symbols can be between -50 and 50, that is to say in the interval [-50; 50] For example, the noise distribution can be a Gaussian distribution.

Preferably, said resulting value is chosen so that the energy of the enlarged watermark does not exceed a predetermined threshold relating to the energy of the host image. In the remainder of the description, it is considered, unless otherwise indicated, that this chosen value is zero. In this case in particular, the predetermined function (applied to the symbols b [i]) can be the sum of the symbols b [i].

Preferably, the noise is added to all the blocks of the watermark, so that the watermarked image has a better visual quality. The blocks are then processed successively according to a predetermined processing order.

The noise can be produced using a random or pseudorandom numbers generator (P) RNG. Pseudo-random generators produce a sequence of mixed bits that depend on an initial seed. This must be initialized with a different value each time it is used. This initial value can be for example the time of the system used, in milliseconds. Each run of the program will use a different seed, resulting in a different random sequence. Conversely, reusing the same seed results in the same pseudo-random bit sequence. Random generators produce sequences of bits in a completely random fashion, the bits being chosen independently and uniformly at random. Each sequence of bits from a new generation is therefore different from the previous ones.

Preferably, according to one embodiment of the invention, if the noise sequence comprises p symbols (p is an integer greater than 1, which is equal in this example to sx ^* sy), only p1 symbols with p1 < p (p1 being an integer greater than or equal to 1) are generated using the generator described above. The remaining p2 symbols (p2 being an integer greater than or equal to 1, with p2 <p) are determined or calculated so that the result of the predetermined function applied to the p symbols is equal to the value chosen for the block considered. It comes p1 + p2 = p. For example, if p = 9, p1 can be chosen equal to 7 and p2 equal to 2.

The predetermined function preferably comprises an addition,; as already indicated, the predetermined function is for example a measure of central tendency (such as an average or a median), or, alternatively, a variance, this list not being limiting. In this case, the chosen value therefore corresponds to a sum, resulting from the addition of the symbols b [i].

If the value chosen is equal to zero, in this case, if the applied function is the average, then the average (and therefore the sum) of the values taken by the noise components for the block considered is zero. The average of the noise components for the whole image is therefore also zero.

The noise components are respectively added to each element of block V so as to obtain the enlarged and noisy watermark W (D4, V, b) as illustrated in figure 7. If D4 = D1, the information can be inserted. in the tattoo image l (D1). If D4> D1, the information must be reduced before being inserted into the image. The inventors noted that the fact of going through dimensions D4 greater than those of the image D1, then of reducing the latter before the insertion of the tattoo, made the visual impact of the tattoo on the tattooed image, more visually acceptable. because homogeneous.

From block to block and from frame to frame, the noise components can take on different values. This is possible by changing the noise generator or the initial seed as explained above. Thus from the same initial tattoo with dimensions D0, it is possible to generate several tattoos to be inserted into different images constituting a video sequence. The tattoo information therefore varies over time, making them very difficult to detect because they do not follow a regular pattern. On the other hand, the energy of the watermark was not reduced because the initial values of the elements were on average not altered.

The invention also relates to a watermarked image according to an embodiment described above.

FIG. 8 represents an example of rendering for a watermark W (D4, V) formed of four elements after enlargement and the enlarged watermark obtained W (D4, V, b), after insertion of the noise of step E231. In this example, the noise generated follows a normal law. Note that the transition between the elements has disappeared after the addition of noise, thus limiting the appearance of adjacent solids in the watermarked image.

FIG. 9 represents an embodiment of an extraction of a watermark from a watermarked image according to the invention, step E14. It is considered that a change of scale has been carried out on the watermarked image considered IW (D2, V, b), the watermarked image from which the watermark must be extracted, having new dimensions D2, i.e. N2 rows and M2 columns , N2 and M2 being positive non-harmful integers. In step E201, an attempt is made to reduce the value of the dimensions of the watermarked image IW (D2, V, b) to the values of the dimensions D0. Indeed, it is in these dimensions that the tattoo can be extracted.

If D2 <D0, the watermarked image IW (D2, V, b) is enlarged to the value of the second dimension D0, for example using the so-called Closest Neighbor interpolation method. We then obtain a scaled watermarked image IW (D0, v, b). The change of scale which was carried out on the watermarked image to bring its dimensions to values less than the D0 dimensions strongly degraded the visual quality of the image, D0 having been preferably chosen to correspond to a standard definition.

If D2> D0, and N2¹nx.N0 or M2¹ny.M0, the watermarked image IW (D2, V, b) is initially enlarged to dimensions D3 (N3 rows and M3 columns, N3 and M3 being higher integers to 1). These dimensions therefore have values greater than the values of the dimensions D2, and preferably the closest, so that N3 = nx.N0 and M3 = ny.M0 (nx and ny being integers greater than 1). This enlargement can for example be carried out using a bilinear algorithm. Thus if the values of the new dimensions are D2 = 960 ^* 800 pixels, those of the second dimensions D0 = 640 ^* 360 pixels, then the watermarked image will be enlarged to the dimensions D3 having 1920 ^* 1080 pixels as values.

If D2> D0 and N2 = nx.N0 and N2 = ny.M0, the dimension of the watermarked image IW (D2, V, b) is not enlarged. Dimensions D3 correspond to dimensions D2.

Then secondly, once the dimensions of the watermarked image have been reduced to multiples of the dimensions D0, these dimensions D3 of the watermarked image can be reduced to the dimensions D0 using the predetermined function. This step will allow the extraction of the watermark with dimensions D0, in particular with the aim of analyzing it, step E201. To obtain the value of the new element v, the predetermined function which was used during the insertion of the watermark in step E 10, is applied to the values of the elements of each block V of the watermarked image with dimensions equal to D3. For example, the predetermined function may include an addition of terms, such as the mean. The value of a pixel of the watermark after reduction is in this case an average sum of the values of the pixels of the block V corresponding to the watermark with dimensions D3. These pixel values of the V block include the values of the noise components that were added during the insertion. tattoo. The sum resulting from the average of these noise components will be close to, or even equal, to the chosen value, for example zero. In this case the value of the pixel of the watermark after reduction is then close to an average sum of the values of the pixels of the block V before the insertion of the noise components. It is equal to it if the transformations undergone by the watermarked image have not had an impact on the values of the noise components added at step E10.

If the chosen value to which is equal the result of the application of the predetermined function to the values of the elements of the block is not zero, step E201 can also comprise for each processed block, a subtraction of said chosen value from the value of the element obtained after the reduction of dimensions. We then obtain a final value of this element v corresponding to an averaged sum of the values of the pixels of the block V before the insertion of the noise components.

The application of the predetermined function, to reduce dimensions, makes it possible to greatly reduce (or even cancel) the noise that had been added during the insertion of the watermark. At the time of extraction, we can then find the watermark W (D0), with for each of its elements, values close to those taken at the end of step E22. It is then possible to analyze it.

When all the blocks of the image to be processed have been processed in a predetermined order, a watermarked image in the second dimension D0 is obtained, the noise which had been added during the insertion of the watermark having been greatly reduced by the application of the predetermined function when changing from dimensions D3 to dimensions D0.

It is then possible to extract the watermark according to a known method described for example in the Digital watermarking manual mentioned above, step E202, then to analyze step E14.

FIG. 10 illustrates a particular way, among several possible, of producing a DIS device configured to implement an embodiment of an assistance method according to the invention. The device DIS comprises a random access memory, for example a RAM memory, an mR processing unit equipped for example with a processor, and controlled by a computer program stored in a read only memory, for example a ROM memory or a hard disk . On initialization, the code instructions of the computer program are for example loaded into the random access memory RAM before being executed by the processor of the processing unit mR. FIG. 10 illustrates only one particular way, among several possible, of producing the device DIS so that it performs certain steps of the method according to the invention. Indeed, these steps can be performed either on a reprogrammable computing machine (a PC computer, a DSP processor or a microcontroller) executing a program comprising a sequence of instructions, or on a dedicated computing machine (for example a set of logic gates such as an FPGA or ASIC, or any other hardware module).

In the case where the processing means is produced with a reprogrammable computing machine, the corresponding program (that is to say the sequence of instructions) may be stored in a storage medium, which may or may not be removable, this storage medium being partially or fully readable by a computer or processor.

The invention therefore also relates to the computer program comprising instructions for implementing the method according to one of the above implementation modes, when said program is executed by a processor.

It goes without saying that the embodiments and embodiments which have been described above have been given purely as an indication and in no way limiting, and that numerous modifications can be easily made by those skilled in the art without however departing from the scope of the invention.

Claims

1. Method for inserting information into a first image comprising N1 rows x M1 columns of elements, N1 and M1 being non-harmful integers, said method comprising the following steps: a) obtaining (E21) from the first image, of a second image comprising NO rows x MO columns of elements, NO and MO being non-zero integers such as N0 £ N1 and M0 £ M1, b) a generation (E22), from the second image, of an initial information comprising NO lines x MO columns of elements, c) an obtaining from the initial information generated, of an intermediate information comprising N4 lines x M4 columns of elements, so that N4³N1 and M4³M1 on the one hand, and N4 = kx.N0 and M4 = ky.M0 on the other hand, N4 and M4 being undamaged integers, kx and ky being integers greater than or equal to 1, said elements of l 'intermediate information being organized in blocks, d) obtaining (E23) said information to be inserted from the intermediate information, comprising ant for at least one block of intermediate information,

a generation of a sequence of symbols representative of a noise, comprising both symbols and elements included in said block, at least one of the symbols being non-zero, so that the result of a predetermined function applied to said symbols is equal to a chosen value,

- an addition of each symbol to the corresponding element of said block, and e) an insertion (E24) of said information obtained in the first image.

2. The method of claim 1, wherein the predetermined function is a measure of central tendency.

3. The method of claim 1, wherein the predetermined function is the mean.

4. The method of claim 1, wherein the predetermined function is the mean.

5. The method of claim 1, wherein said selected value is equal to zero, kx or ky being greater than or equal to 2.

6. The method of claim 1, wherein the intermediate information is obtained from the initial information by means of a magnification method.

7. The method of claim 1, wherein if N4> N1 or if M4> M1, obtaining the information to be inserted further comprises, following the addition of each symbol to the corresponding element of said block, a reduction of the size of the intermediate information so as to obtain respectively N4 = N1 or M4 = M1.

8. The method of claim 1, wherein said sequence of symbols representative of the noise comprises p symbols, such that p1 symbols are generated randomly or pseudo-randomly and p2 symbols are calculated so that the result of the predetermined function applied to the p symbols, or equal to said chosen value, p, p1 and p2 being integers such that p = p1 + p2.

9. A method of extracting information formed from a plurality of elements comprising NO rows and MO columns, inserted into an image comprising N2 rows x M2 columns of elements using the insertion method according to one of the following. claims 1 to 8, NO, MO, N2 and M2 being non-harmful integers, such as N2> N0 and M2> M0, said method of insertion comprising the following steps: f) obtaining from said image, of a new image comprising N3 rows and M3 columns of elements, with N3³N2 and M3³M2 on the one hand, and N3 = nx.N0 and M3 = ny.M0 on the other hand, N3 and M3 being undamaged positive integers, nx and ny being integers greater than 1, the elements of said new image being organized in blocks, g) obtaining (E201) a reduced image from the new image, the reduced image comprising NO rows x MO columns elements, each element of the reduced image being obtained from the elements of a corresponding block in the new image, and for each element of the reduced image to obtain:

a determination of the value of the element considered by applying said predetermined function to the values of the elements of the block of the new image corresponding to said element, the value of said element considered corresponding to the result of the application of the function, and h) an extraction (E202) of the information from the reduced image.

10. Device for inserting information into a first image comprising N1 lines x M1 columns of elements, N1 and M1 being undamaged integers, the device being configured to implement the following steps: i) obtaining at from the first image, from a second image comprising NO rows x MO columns of elements, NO and MO being non-zero integers such as N0 £ N1 and M0 £ M1, j) one generation, from the second image, of an initial information comprising NO lines x MO columns of elements, k) an obtaining from the initial information generated, of an intermediate information comprising N4 lines x M4 columns of elements, so that N4³N1 and M4³M1 on the one hand, and N4 = kx.N0 and M4 = ky.M0 on the other hand, N4 and M4 being non-harmful integers, kx and ky being integers greater than or equal to 1, said information elements intermediary being organized in blocks,

L) obtaining said information to be inserted from the intermediate information, including at least one block of the intermediate information

11. Device for extracting information formed from a plurality of elements comprising NO rows and MO columns, inserted into an image comprising N2 rows x M2 columns of elements using the insertion method according to one of claims 1 to 8, NO, MO, N2 and M2 being undamaged integers, such as N2> N0 and M2> M0, the device being configured to implement the following steps: n) obtaining from said image, from a new image comprising N3 rows and M3 columns of elements, with N3³N2 and M3³M2 on the one hand, and N3 = nx.N0 and M3 = ny.M0 on the other hand, N3 and M3 being non-harmful positive integers, nx and ny being integers greater than 1, the elements of said new image being organized in blocks, o) obtaining a reduced image from the new image, the reduced image comprising NO rows x MO columns of elements, each element of the reduced image being obtained from the elements of a corresponding block in the new image, and for each element of the reduced image to obtain :

a determination of the value of the element considered by applying said predetermined function to the values of the elements of the block of the new image corresponding to said element, the value of said element considered corresponding to the result of the application of the function, and p) an extraction of information from the reduced image.

12. A computer readable recording medium, on which is recorded a computer program comprising program code instructions for carrying out the steps of the method according to any one of claims 1 to 9.