That strongly depends on the ratio of covert to overt data. There is some math theorem in theory of communication that deals with the amount of noise (Shannon - Mathematical Theory of Communication, I think). If you operate under that ratio, and have a good conventional crypto to give you the positions of bits that carry information instead of the noise, even the best equipped adversary cannot find anything without knowing of the key - and we’re back on the floor of conventional crypto where secrecy depends or should) on the key only.
If you manage to squeeze this into a library for handling e.g. video or audio compression, then you can exploit existing comm apps; nothing in the comm protocol then will look as something out of ordinary and you’ll have a wide choice of covert channels.
