Patent ID: 8121339

Claim:
A method of encoding a message comprising a plurality of bits into a document, the document containing known information, the method comprising the steps of: identifying a plurality of logical information content categories associated with the known information; establishing a priority order of the categories in which the message is to be encoded in each of the categories; determining an amount of the message to be encoded in each of the categories based upon the established priority order; and encoding the message into the document for each identified category and the corresponding determined amount of the message by: selecting a plurality of adaptive marks from a set of predefined adaptive marks, the selection being based upon a characteristic of the known information around a location where the selected adaptive marks are to be used, to maximize contrast between a first part of the selected adaptive marks and a second part of the selected adaptive marks and to minimize contrast between the selected adaptive marks and the known information around the location; and incorporating at least one selected adaptive mark into the document in accordance with bits of the corresponding determined amount of the message.