It really depends on your country. I got already trouble coz a Member did upload a Avatar image that was under Copyright. Of course, its impossible to control all the user content. Even Text can have a Copyright. I think if you remove it imitatively after u know its not allowed and do your responsibility as a webmaster they can't sue you.

It's a big & easy business for the lawers. It's always better being careful and try to avoid any possible trouble.