Now, usually creating fan art grants you the Creative Commons License in which you have sole ownership and trademark over what you yourself has created. Still, license or not, that won't stop art thieves or copycats from stealing your hard work.
You can't legally sell fan art--even if you created it yourself. So you wouldn't be able to legally profit from it regardless. Creative Commons basically says "I made this, but you can use it, and also the original creator of the copy-righted material can't sue you (or me) for it. So why does it even matter if someone 'steals' it. What the heck are they going to do with it? You can't legally sell it. They can't legally sell it. Why does ownership even really matter at that point? Fan art should be about fun and doing something you enjoy because you have a passion for it or the character you want to pay tribute to.

Art is always so weird. I'm an artist too, and I've never felt offended when people steal or use my work. I do (non-fan) art because making art is fun. Whatever happens to it after I'm done with it--I could care less. But It always comes off as super hypocritical when people cry bloody murder about stolen art, and yet half their portfolio is fan-art of copy-righted characters.

Ah, you got me all ranty. ^.^ I still love art, but the art community just pisses me off sometimes. It's like somewhere along the lines people stop doing art as a passion, and it becomes an ego-trip. Such a buzz-kill. I never copy/trace/fan-art, because those things are boring to me. But if another artist wants to--why hate on them? Art is about fun. And once you get into copy-right/fan-art territory--no one should have the right to talk down to those folks, because y'all stealing at that point. Live and let live.