Great article on Time.com: http://time.com/3615271/facebook-privacy-policy-photos/
The quick-and-dirty synopsis: photographers everywhere have been paranoid about Facebook stealing their photos and supposedly absorbing the copyrights once they're posted on their site. They also think that by writing a one line passage on their wall, it mitigates their terms of service, thus bypassing the end-user-licensing agreement. Time has revealed that Facebook needs to have the clause in their terms, otherwise images can't be posted or shared on their site, and it doesn't even come close to addressing copyright. Just know this photographers, Facebook doesn't absorb your copyright once you post something on Facebook.