I imagine it would be similar to any site based on user generated content where they would first need to contractually prohibit users from uploading material that infringes on third party intellectual property rights and then they would need to have a policy in place to address any complaints by third party intellectual property rights holders that their right were being infringed. But it certainly wouldn't be a safe bet to just assume their off the hook entirely because it's too hard for them to determine infringement.