Depends.
1. Limited sales of content. Good record keeping on who has model releases.
2. If model I.D.'s are released. Void contract. No refund. Sue per terms outlined IN model release.
3. Go after site, image host, etc for site providing backbone to posting I.D.. Track down poster.
There are many things you can, and could do. Both in prevention, and enforcement.
However, my bet is most of the people responding to this thread will say the models signed up for this to get the quick cash, so fuck em. They knew what they were in for when signing the release.
