Coming from the artists' corner of fandom, for once...
Claiming copied fanart as your own might be bad, but talking about that in public is worse. Many delicate issues definitely worth considering can arise to trouble you in an internet community, after all.

What if people opened lawsuits over you defaming their character as you wrongfully accused them in a Livejournal community of tracing other people's anime fanart at internet doodle boards? What if it would make crazed vigilantes gather to torch the accused person's house? Would you knowingly scar the emotionally retarded artists?

Rah, just one week after I get accepted into Elfwood I'm already getting my lunatic flamewar fix.