Offer the ability for DMCA take downs.. that is ALL you are required to do after posting all your disclaimers and putting the uploading on the members. But seriously, give me a break, if I google to find images I am NOT going to try to track down through 50 various hops .. to find the original copyright holder in order to get permission to edit some post or image that became part of the public pop culture awareness as soon as it was posted to the WORLD WIDE WEB and seen by the globe's population in a heartbeat knowing it will forever remain available ON the same world wide web almost forever. So.. am I gonna ask permission or ask for forgiveness later? If you agree to remove something, that is almost always enough to make amends. And please.. don't forget fair use as long as you are not using an entire work, talk to a lawyer and iron this stuff out, don't put it all on the contributors.