Watermarking images with wavepackets encoded by intensity and/or phase variations
View Patent ↗A phase space encoded watermark is applied to an image to guard against counterfeiting and/or unauthorized copying. The watermark is formed of wavepackets. An authentication message is encoded in the wavepackets by variations in one or both of the intensities of the wavepackets and the phases of the wavepackets.
1. 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.
2. The method according to claim 1 , further comprising:
transforming pixel values of the combined image data before the combined image data is printed.
3. The method according to claim 1 , wherein the image is printed as part of a postage meter indicium.
4. The method according to claim 1 , wherein the second message string represents an encrypted message.