JPEG Based Conditional Entropy Coding for Correlated Steganography

Correlated steganography considers the case in which the cover work is chosen to be correlated with the covert message that is to be hidden. The advantage of this is that, at least theoretically, the number of bits needed to encode the hidden message can be considerably reduced since it is based on the conditional entropy of the message given the cover. This may be much less than the entropy of the message itself. And if the number of bits needed to embed the hidden message is significantly reduced, then it is more likely that the steganographic algorithm will be secure, i.e. undetectable. In this paper, we describe an example of correlated steganography. Specifically, we are interested in embedding a covert image into a cover image. Comparative experiments indicate that selecting a cover Work that is correlated with the covert message can reduce the number of bits needed to represent the covert image below that needed by standard JPEG compression, provided the two images are sufficiently correlated.