The process is similar to the user assisted face control. Users can approve/reject photos and a decision is made based on the majority of the votes. If the results are close to 50/50 then the photo is marked for manual approval by administrator. Users who are often making wrong choices will soon have the option disabled for them and users who are helping the most can participate in the "Top Moderators" chart. The chart is a good way to motivate the users to assist you and you can throw a bonus for the top moderator for extra motivation.