Minor correction - steganography - one of my favorite subjects.

A variant: I once made, but did not post, a pair of images that looked like nonsense. When you xor'ed them, and saved the file as mp3, you got a popular copyrighted song. I never did it in practice, but it is theoretically incredibly easy.

I suppose each was what you'd call a "derivative work" but you'd be hard pressed to prove either one by itself was so.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)