etriplex

This might be dumb and I might be over thinking it but I am starting a new site and I want all the pictures to come from them so they are real self pics. My question is. How can I do this legaly since I am not taking the photos? Do still have them to sign a modeling contract and take a copy of their ID or do the need to sign some kind of documents signing over the photos? If someone could tell me how to do this that would be great!