Since users can upload music, video, and pics. I would maybe like to see a check box that says something along the lines of "By checking this box I certify that i own the content i am posting or it is legal for me to do so" Just to cover the webmaster. What does everyone else think? Also maybe a NSFW box for filtering options? IDK just throwing out some ideas.
Just like FB, Twitter, google+ and many other social networking sites, you can also dedicate a page for terms and conditions which will automatically imply that if a user is uploading a photo/video/music file, he/she agrees that the content is solely his/hers to begin with and does not violates any copyright.
Otherwise we can make a function for your requirement but it will only make it harder for people to upload media files.
you are right. It is already in my terms when they sign up i believe.