Variable message coding protocols for encoding auxiliary data in media signals

A method of decoding a digital watermark having fixed and variable protocol message portions, the method comprising:

• extracting a hidden message code embedded in modification of a host media signal by evaluating the host media signal to compute the hidden message code having the fixed and variable message protocol portions;
• performing error robustness decoding of the fixed protocol portion of the extracted message code to produce one or more message symbols representing a version identifier;
• interpreting the version identifier to ascertain a version of variable protocol used to embed the variable protocol portion;
• and
• applying an error robustness decoding method of the version to decode message symbols of the variable message protocol portion.

A message protocol method for steganographically encoding a variable message into a media signal, the method comprising:

• forming a control message portion including at least one symbol that identifies the format of the variable message;
• forming a variable message according to the format, wherein the format indicates a variable length of the variable message portion;
• and
• producing a media signal with the variable message steganographically encoded in the media signal by altering the media signal such that the variable message is not discernable by a human but is readable by an automated reader.