If (b) and (c) can be considered derivative works, then should a low-bit hash of (a) not also be considered a derivative? If a given hashing algorithm says the hash of Metallica's latest hit is 42, have I just broken the law by posting this?
It's not just a yes/no on derivation, the amount of information present in the derivative data matters. If you hashed every 32 bits individually then you would be infringing, but one hash for the whole thing is fine.
