Patent ID: 7710551

Claim:
A method for authenticating a device subject to counterfeiting attempts, said device being selected from a set of security documents and valuable products, said device comprising a base layer superposed with a revealing layer sampling said base layer, the method comprising the steps of: a) observing a superposition of said base layer comprising a base band grating and said revealing layer comprising a revealing line grating, said superposition forming a moire layer comprising a band moire image and b) comparing said band moire image with a reference band moire image and depending on the result of the comparison, accepting or rejecting the device, where said base band grating comprises in each base band a non-repetitive sequence of base band patterns having shapes derived from elements selected from a set of typographic characters, logos, symbols, signs, line art and graphical elements, where respective layouts of the base band grating, the revealing line grating and the band moiré image are related according to a band moiré image layout model, said band moiré image layout model enabling to choose the layout of said revealing line grating and of said band moiré image and obtain the layout of said base band granting by computation on a computing system, where said band moire image comprises band moire patterns whose shapes are enlarged and transformed instances of said base band pattern shapes and where said observation and comparison steps are carried out by a person.