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Digital watermark methods for encoding auxiliary data into a host signal are used to authenticate physical and electronic objects. One such method computes a content specific message dependent on the host signal, encodes the content specific message into a watermark signal, and embeds the watermark

Digital watermark methods for encoding auxiliary data into a host signal are used to authenticate physical and electronic objects. One such method computes a content specific message dependent on the host signal, encodes the content specific message into a watermark signal, and embeds the watermark in the host signal such that the watermark signal is substantially imperceptible in the host signal. One specific implementation embeds data representing salient features of the host signal into the watermark. For example, for photo IDs, the method embeds the spatial location of salient features of the photo into the watermark.

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1. A method comprising: providing a plural-symbol watermark message;computing via a processor a watermark key that is dependent on an attribute associated with a host signal, or with an object used to convey the host signal, wherein the attribute is configured to associate the host signal or object

1. A method comprising: providing a plural-symbol watermark message;computing via a processor a watermark key that is dependent on an attribute associated with a host signal, or with an object used to convey the host signal, wherein the attribute is configured to associate the host signal or object with a proprietor; andembedding the watermark message in the host signal such that the watermark signal is substantially imperceptible in the host signal;wherein the watermark key specifies how or where the watermark message is embedded in the host signal. 2. The method of claim h wherein the attribute comprises a name of an individual. 3. The method of claim 2, further comprising converting the name of an individual with a predetermined function, and computing the watermark key based thereon. 4. The method of claim 2, further comprising indexing a data store using information related to the name of the individual, to retrieve information associated therewith, and computing the watermark key based on the retrieved information. 5. The method of claim 1, wherein the watermark key specifies a temporal location of the watermark message in the host signal. 6. The method of claim 1, wherein the watermark key specifies a spatial location of the watermark message in the host signal. 7. The method of claim 1, wherein the watermark key specifies host signal transform coefficients that are altered to encode the watermark message. 8. The method of claim 1, wherein the symbols comprising the watermark message are not dependent on the host signal. 9. The method of claim 1, wherein the watermark key specifies how the watermark message is embedded in the host signal. 10. The method of claim 1, wherein the watermark key specifies where the watermark message is embedded in the host signal. 11. An apparatus comprising: an input configured to receive a plural-symbol watermark message;means for computing a watermark key that is dependent on an attribute associated with the host signal, or with an object used to convey the host signal, wherein the attribute is configured to associate the host signal or object with a proprietor; andmeans for embedding the watermark message in the host signal such that the watermark signal is substantially imperceptible in the host signal;wherein the watermark key specifies how or where the watermark message is embedded in the host signal. 12. The apparatus of claim 11, wherein the watermark key specifies where the watermark message is embedded in the host signal. 13. The apparatus of claim 11, wherein the watermark key specifies how the watermark message is embedded in the host signal. 14. An apparatus comprising: an input configured to receive a plural-symbol watermark message; anda processor configured to:compute a watermark key that is dependent on an attribute associated with a host signal, or with an object used to convey the host signal, wherein the attribute is configured to associate the host signal or object with a proprietor; andembed the watermark message in the host signal such that the watermark signal is substantially imperceptible in the host signal;wherein the watermark key specifies how or where the watermark message is embedded in the host signal. 15. The apparatus of claim 14, wherein the watermark key specifies where the watermark message is embedded in the host signal. 16. The apparatus of claim 14, wherein the watermark key specifies how the watermark message is embedded in the host signal. 17. A non-transitory computer readable medium comprising instructions, the instruction comprising: instructions to compute a watermark key that is dependent on an attribute associated with a host signal, or with an object used to convey the host signal, said attribute serving to associate the host signal or object with a proprietor; andinstructions to embed a plural-symbol watermark message in the host signal such that the watermark signal is substantially imperceptible in the host signal;wherein the watermark key specifies how or where the watermark message is embedded in the host signal. 18. The non-transitory computer readable medium of claim 17 wherein the watermark key specifies where the watermark message is embedded in the host signal. 19. The non-transitory computer readable medium of claim 17, wherein the watermark key specifies how the watermark message is embedded in the host signal.