1. Terminology

Steganography refers to the concealment of messages, but this can take several forms which, in some cases, need to be distinguished. The term "information hiding" is used to refer to all aspects of concealing information:

• steganography in the strict sense of the term, i.e. concealment with the aim of keeping the existence of the communication confidential;

• techniques for anonymizing communications ;

• watermarking ;

• watermarks (fingerprinting).

The question of anonymity calls for slightly different techniques, and we won't go into that here, but it is generally accepted that this issue comes under the heading of information hiding. Watermarking refers to the insertion of marks designed to identify the rightful...