As frustrating as my brush with Marvel's legal department was years ago, the litigation wars are escalating much further, much faster.
Because this is (or at least, was) a business, I am in a much more tenuous legal position than you are as individuals. And yet, here's a case where a guy did some cool Wolverine sketches and had to hire a lawyer to keep Marvel from retroactively taking them for their own.
Make versions of copyrighted characters at your own risk, folks. But if you do, you can't post them here.