from the README:

OutGuess is a universal steganographic tool that allows the insertion
of hidden information into the redundant bits of data sources.  The
nature of the data source is irrelevant to the core of OutGuess.  The
program relies on data specific handlers that will extract redundant
bits and write them back after modification.  In this version the PNM
and JPEG image formats are supported.

WWW:  http://www.outguess.org/

Trevor Johnson
trevor@FreeBSD.org