Steganography capacity: a steganalysis perspective

Two fundamental questions in steganography are addressed in this paper, namely, (a) definition of steganography security and (b) definition of steganographic capacity. Since the main goal of steganography is covert communications, we argue that these definitions must be dependent on the type of steganalysis detector employed to break the embedding algorithm. We propose new definitions for security and capacity in the presence of a steganalyst. The intuition and mathematical notions supporting these definitions are described. Some numerical examples are also presented to illustrate the need for this investigation.