Automated systems have been being used to detect sexual content for a while now using visual strategies. Chatroulette, for example, got fed up with being associated with the flashers that infested their site, so they developed an algorithm to doggedly search for penises and automatically ban their owners. These algorithms usually look for a lot of skin on-screen, but have problems with false positives.
Now they're going a step further, employing techniques using audio analysis. So if you have been relying on Avatar porn to get around your employer's color based filters, watch your back.