If you had it so anyone posting or sharing their uploads had to accept the terms of service, and also in the terms state that anyone finding any of their copyrighted work they can submit a copyright infringement notice and it will removed if their claim is found to be correct.
You would then only be liable to any legal issues if you did not adhere and ignored the request to take down the copyrighted material
Racedepartment.com have the same for their site
"Intellectual Property and Copyright
If you believe your copyright-protected work was posted on RaceDepartment by one of our users without authorization, you may submit a copyright infringement notification. These requests should only be submitted by the copyright owner or an agent authorized to act on the owner’s behalf. The fastest and easiest way to notify RaceDepartment of alleged copyright infringement is to either use the “report” button, located under each forum post or resource file, or contact us directly via email.
Posts, attachments, uploads or links which contain original game files are not allowed."