29. You know, I can't recall off the top of my head if I've seen someone slap huge watermarks over their fanart (though I'm sure I have), I can understand the logic behind it. I don't know if they're trying to stop other people from posting it elsewhere, necessarily, but rather they want to avoid other people posting it and taking credit for their work. It's harder to pull that off if someone were to try stealing art of original characters, but I've seen people post stolen fanart and claim it as their own.

As an artist, it's frustrating to see people take credit for someone else's hard work! So I'm assuming that most people slap watermarks across their pictures to avoid that happening. Not that it'll deter art thieves entirely (someone once took art of mine and reposted it with my signature on the piece still intact!).