Patent ID: 7551751

Claim:
A method of applying a fragile watermark to an image, the method comprising: (a) providing image data that represents the image; (b) providing a first message string that includes a first plurality of message bits and a second message string that includes a second plurality of message bits; (c) arraying the message bits of the first message string at points of a four-dimensional lattice, the four-dimensional lattice being formed as a product of a two-dimensional position-domain lattice and a two-dimensional frequency-domain lattice; (d) generating wavepacket data by convolving each of the message bits of the first message string with a respective watermark function in accordance with a position of the respective bit of the first message string in the four-dimensional lattice, thereby forming data corresponding to a respective wavepacket for each “1” bit of the first message string; (e) modifying at least one of an intensity level and a phase of the respective wavepacket data for at least some of the “1”, bits of the first message string to encode in the wavepacket data a message which corresponds to the second message string; (f) combining the modified wavepacket data generated at step (e) with the image data provided at step (a) to generate combined image data; and (g) printing the combined image data to produce the fragile watermark image so that the fragile watermark will be degraded when the fragile watermark image is scanned and reprinted.