I'm roaming around the Web looking up stuff on patenting business methods and algorithms and I stumble across this from iChris.ws:
It's an illustration from U.S. patent 6,751,348, "Automated detection of pornographic images."
- Compare each pixel's color with library of skin colours (white/black/etc.)
- If it's single pixel, it's ok. If it's an area of skin color, it's probably skin.
- Using some algorithm to determine if it's a face or not. If it's just face, it's probably portrait, which is ok.
- Determine from the shape which body part(s) is exposed.
- Determine if the post is erotic.
Amusing aimless thought process: start thinking of ways in which the algorithm could be spoofed. No. 5 is no easy determination to make, whether by software or by wetware.