If the tile is modified to the point that the original work is completely unrecognizable in the result and there's virtually none of the original tile left, I believe that the distribution of the result is allowable under fair use (arguing that the remaining creative component from the original is so miniscule as to be negligible and insignificant). This is ignoring attributes like "
22x22 tile with a gray-192 background"
, which would be specification information and not creative.
IMHO, the one on the right is pretty clearly derived from the Beethro tiles and I don't think that one's okay. I wouldn't venture an opinion on the one on the left.
Also, in my estimation, posting the tiles here for the purposes of constructive discussion falls under fair use -- commentary and discussion on copyright work is allowable. One wouldn't be justified in taking these tiles and using them in their hold, though, but having them here for discussion is I believe okay.
Of course, IANAL and you may not rely on any of this as definitive. All standard disclaimers apply.
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I was charged with conspiracy to commit jay-walking, and accessory to changing lanes without signaling after the fact
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++Adam H. Peterson