Decoding steganographic messages embedded in media signals

A method of decoding a message embedded into a host signal, where the message is encoded in a two-dimensional code signal inserted into the host signal to form a composite signal and symbols in the message have predetermined signal characteristics, the method comprising:

• receiving a potentially modified version of the composite signal;
• and correlating the predetermined signal characteristics with the potentially modified composite signal to decode message symbols;
• decoding the message without using the host signal;
• estimating at least portions of the host signal;
• and
• removing an estimate of at least portions of the host signal before decoding the message.

A method of decoding a message steganographically embedded into a host signal, where the message is embedded into the host signal to form a composite signal in which the message is substantially imperceptible by adjusting the host signal to encode signal characteristics associated with message symbols, the method comprising:

• analyzing a potentially modified version of the composite signal to gather evidence of the characteristics associated with the message symbols in the message, including estimating at least portions of the host signal, and removing an estimate of at least portions of the host signal to compute an estimate of steganographically embedded data;
• and
• based on the evidence, estimating message symbols in the steganographically embedded data;
• and
• comparing the estimated message symbols with one or more message symbols known to be included in the message to assess whether the potentially modified version of the composite signal has a valid message.