Techincally, every image created by a person and posted is copyright protected. With that said, unless a person registers it with the copyright office, they aren't likely to sue you. They would have to prove damages. If it's not registered, they can't collect attorney's fees, so the risk reward isn't there.
It's usually common courtesy to ask permission, especially if you want to use images from fellow members, even if you want to use them on, say, ebay. It's when people steal other people's images and use them on the same site to sell the same type of item (ebay for example), therefore competing with the person whose image was stolen, that there is a real issue. Using a person's image then competing with them is really not cool.
I can speak from experience on this, having just gone through a Federal Copyright Infringement Lawsuit against a person who raided my commercial site and was using it for his own benefit. He's probably on the verge of bankruptcy right now, and deservedly so. Rather than try to work it out, he told me to F off. Bad mistake. Let's just say I won, and he's regretting the F Off attitude and will likely re-evaluate future responses like that.
