Media and methods employing steganographic marking
Stationery, or other printable media, is encoded with a digital watermark. The watermark is not conspicuous to a human observer of the media, yet conveys plural bits of auxiliary information when optically scanned and digitally processed. The watermark can be formed by ink-jet printing, or otherwise. The encoded information can be used for various purposes, including authenticating the document as an original, linking to associated on-line resources, and distinguishing seemingly-identical versions of the same document (document serialization).
1. A substrate useful in forming a printed object, characterized in that the substrate has been marked to encode a steganographic digital watermark pattern thereon that conveys plural bits of digital information, said marking not being apparent to a human observer of the printed object, said steganographic pattern being detectable by visible-light scanning of the printed object to yield data from which the plural bits of digital information can be recovered, wherein said plural bits of digital information correspond to the digital watermark pattern in accordance with an algorithmic transformation, and the marking comprises a speckling of ink dots.
2. The substrate of claim 1 wherein said processing locally changes an ink absorption attribute of the substrate.
3. The substrate of claim 1 wherein the digital watermark pattern degrades when photocopied, so that the printed object can be distinguished from a photocopy thereof.
4. The substrate of claim 3 comprising a second digital watermark pattern, the second pattern being robust against photocopying.
5. The substrate of claim 1 wherein said plural bits of digital information comprise an identifier, said identifier serving to convey information indicative of an electronic address.
6. The substrate of claim 5 in which the identifier comprises a pointer into a remote data structure, the remote data structure storing an electronic address corresponding to said substrate.
7. The substrate of claim 1 , wherein the substrate comprises blank printing stock.
8. The substrate of claim 1 , wherein the marking comprises a speckling of ink dots in a regular array.
9. The substrate of claim 1 , wherein the marking comprises a speckling of opaque ink dots in a regular array.
10. The substrate of claim 1 , wherein the marking comprises a speckling of ink dots in an apparently random array.
11. The substrate of claim 1 , wherein the marking comprises a speckling of opaque ink dots in a regular array.
12. The substrate of claim 1 , formed into a printed package.
13. The substrate of claim 1 wherein said plural bits of digital information serve as a pointer into a remote data structure.
14. The substrate of claim 1 wherein the substrate is blank except for the speckling of ink dots.
15. The substrate of claim 1 wherein at least certain of said ink dots are on a vacant region of substrate to which no other printing pattern is applied.
16. The substrate of claim 1 wherein the steganographic digital watermark pattern is repeated in tiled fashion across at least a part of the substrate.
17. The substrate of claim 1 wherein said plural bits of digital information correspond to the digital watermark pattern in accordance with an algorithmic transformation and a cryptographic key.
18. The substrate of claim 1 wherein each of the dots decreases local luminance of the substrate.
19. The substrate of claim 1 formed into a printed package, wherein:
said plural bits of digital information correspond to the digital watermark pattern in accordance with an algorithmic transformation and a cryptographic key; and
at least certain of the ink dots are on a region of the package to which no other printing pattern is applied.
20. A method of processing a blank substrate prior to formation of a printed object, the method comprising encoding the substrate with a steganographic digital watermark pattern that does not impair subsequent use of the substrate, yet conveys plural-bit digital information, said pattern not being apparent to a human observer of the printed object, said steganographic pattern being detectable by visible-light scanning of the printed object to yield data from which the plural bit digital information can be recovered, wherein said plural bits of digital information correspond to the digital watermark pattern in accordance with an algorithmic transformation.
21. The method of claim 20 wherein the digital watermark pattern is designed to degrade when photocopied, so that the original printed object can be distinguished from a photocopy thereof.
22. A method comprising:
applying an algorithmic transformation to plural bits of digital information to generate pattern data corresponding thereto;
marking a substrate with dots of ink to encode a steganographic pattern thereon corresponding to said pattern data;
wherein said marking is not apparent to a human observer of the marked substrate, but the plural bits of digital information are decodable from visible light scan data captured from the marked substrate.
23. The method of claim 22 wherein the substrate includes a visible printing design, and the method includes overprinting the dots of ink thereon.