I was thinking about developing a small community website where people of a certain profession can register and post their own blogs (Which includes an optional photo). I then got to thinking about how people might use this and the fact that if they are given the option to add a photo, they might be likely to use one that they simply find on Google, another social network or even an existing online blog/magazine article. So how do I cover myself from getting a fine slapped on me and to make it purely the fault of the individual uploader?

I plan on having an option where the user can credit a photo by typing in the original photographers name & web link (optional) and to make them tick a check box stating that the post is their own content and that they have permission to use any images but is that enough to cover myself? How do other sites do it?