I'm always a little torn on this one. On one hand, it's great when credit is given and it sucks when someone else claims to be the source on something that you took the time to find and upload. On the other hand, I'm happy to see stuff I upload spread around the internet. It's not like I'm the original creator of a bulk of the content I put online, I just took the time to digitally preserve it and upload it. Since I'm not the original creator, I don't watermark anything. I think it'd kind of a slap in the face of the original developers to watermark a screenshot from their game or to the writers of a magazine to watermark a scan of one of their pages. It's a reason why I don't upload too much stuff to MobyGames and why I uploaded so much to GiantBomb instead. I think the best solution is to just add some metadata to all of your images. You get to keep the clean originals without any silly logos or anything on them, and you also get to have a little digital tag showing the source of the file. 99.999% of the people that mirror images never bother to touch the metadata (or even look if it's there) before rehosting them. Don't get too worked up over people mirroring stuff. That's the nature of the internet and helps ensure data remains decentralized, preserved, and available.
Let's be realistic. No one ever cares about the poster or source of torrents. I download Japanese tv shows and I don't remember any of the posters, though I am thankful.
