I'm actually having a similar problem myself. According to someone I know there was a thread on 2ch.ru where some boobs discussed where to post CP and apparently my board was a target.

Luckily I catch it within 24 hours of it being posted but it's still really infuriating; I find it abhorrent, I have to take the time to clean it up, and it could land me in some kind of trouble with my host or law enforcement.

Based on IPs the posters are obviously cycling proxies so banning is a waste of time.

An md5 blacklist is a good idea in theory but who the hell is going to compile that? Of course if the poster really wants to be a boob he or she could just make a slight modification to the image.

>Proxy checks are not reliable.

Better than nothing?