I know it's based on at least keywords and in-bound link anchors, and for images they do some image recognition. Now the problem is, it's complete traffic killer when you drop of the safe search as other adult sites still continue to be in main index. Users don't either know how to put safe search off or don't care as they still get results. Now, adult keywords obviously bring a lot of traffic, so you can't completely abandon their either. The question is, how do you keep a fine line between staying in safe search and still use the keywords in a way you continue to rank well?