There is a less naive steganography tool in the Debian repos named steghide. According to the manual: Steghide uses a graph-theoretic approach to stegan

There is a less naive steganography tool in the Debian repos named steghide. According to the manual: Steghide uses a graph-theoretic approach to steganography. You do not need to know anything about graph theory to use steghide and you can safely skip the rest of this paragraph if you are not interested in the technical details. The embedding algorithm roughly works as fol‐ lows: At first, the secret data is compressed and encrypted. Then a sequence of postions of pixels in the cover file is created based on a pseudo-random number generator initialized with the passphrase (the secret data will be embedded in the pixels at these positions). Of these positions those that do not need to be changed (because they already contain the correct value by chance) are sorted out. Then a graph-theoretic matching algorithm finds pairs of positions such that exchanging their values has the effect of embedding the corresponding part of the secret data. If the algorithm cannot find any more such pairs all exchanges are actually performed. The pixels at the remaining positions (the positions that are not part of such a pair) are also modified to contain the embedded data (but this is done by overwriting them, not by exchanging them with other pixels). The fact that (most of) the embedding is done by exchanging pixel values implies that the first-order statistics (i.e. the number of times a color occurs in the picture) is not changed. For audio files the algorithm is the same, except that audio samples are used instead of pixels. I wonder how hard it would be to detect (not decode) content hidden by steghide.