I've personally noticed that ~80% of the griefers on my servers have the iconic "edgy teenager" skin applied, or the "headphone skin".
After performing some experimentation with thresholding (gave up on OpenCV because detail just isn't there), I've found that a threshold value of 160, applied on popular skins, results in an almost perfect match for detecting "edgy teenager" skins:
This plugin, when released, will provide configurable options for skin recognition, and configurable actions for each specific skin type.
Using some image processing, I hope that this can drastically reduce the amount of immature kids on your server.