Methods for encoding a source color illustration, for authenticating an illustration, and related computer media

A method for encoding a source color illustration, the method comprising:

• inscribing a source color illustration in a form of an illustration inscribed in grayscale or in color;
• encoding a message in a form of a two-dimensional barcode comprising a set of blocks, each block of the set of blocks coding a fragment of the message and comprising a set of (M) rows and (N) columns, and each block of the set of blocks comprising a set of coding subblocks, each coding subblock of the set of coding subblocks comprising a set of bits, the encoding comprising:
• defining or identifying a set of distinctive points in the source color illustration, a distinctive point, of the set of distinctive points, being a pixel or a set of two-by-two adjacent pixels for which a contrast gradient, in one direction and at a predefined distance, is greater than a predefined threshold value;
• calculating a set of attributes according to at least some of the distinctive points of the set of distinctive points to form a set of calculated attributes;
• selecting, from among the set of calculated attributes, a set of at least one attribute to define a digital fingerprint;
• and
• recording in the message one among:
• the set of the at least one attribute;
• the digital fingerprint;
• the digital fingerprint as a compressed digital fingerprint;
• the digital fingerprint as an uncompressed signed digital fingerprint, fingerprint;
• and
• the digital fingerprint as a compressed signed digital fingerprint;
• with the source color illustration not already in digital form, digitizing the source color illustration to form a digitized source illustration;
• decomposing the digitized source illustration into a set of areas, each area of the set of areas being defined by:
• a primitive, determined by a shape recognition algorithm, a biometric recognition algorithm, or a color gradient;
• an edge detection algorithm;
• or
• applying to the source color illustration a static geometric grid having a predetermined shape, the static geometric grid comprising the set of areas;
• associating with each area, of the set of areas, a respective color or item of color information;
• and
• encoding at least one of the items of color information of the source color illustration in the two-dimensional barcode.