I recently had to ban a few members for plagiarism issues. It's something I don't like to do but when people keep submitting stuff with fan art, after I've warned them a few times not to, I have to. So I'm going to highlight how important it is to be more careful with choosing a site to get images from.
I'm going to use zerochan as an example since it's one of the biggest offenders I see these days. People find stuff there and don't realize it's more like photobucket and not a site for hosting scans. People simply upload whatever they find and like.
Now one of the things that should be a huge red flag is if the dimensions of what is hosted is wallpaper size or if there is any form of signature on it. Chances are, this will mean it's a wallpaper taken from somewhere else and hosted there. A signature can be a clear indicator that it's fan art.
Also if you see things like Pixiv or DA in the tags. Those sites host massive amounts of fan art, something you want to avoid. If you can't find anything to indicate one way or the other, simply do not use it. It's better to be safe than sorry.
There are sites out there that have huge sections of scanned works. Like Animepaper and MiniTokyo for example. We even have members like Desbreko who have imageshack accounts with thousands of screenshots from anime shows that you can use for making e-cards.
We try to give people a chance since we know using fan art is going to happen. But at the same time we do expect people to actively try to get informed and to be responsible about where they are getting stuff from.
Anyway if any of you have other tips or questions definitely bring it up in the comments. Thanks.