[michaelcampbell]

I may have misread, but wasn't the "clever bit" the part that tried to detect if an image was pornographic? (As opposed to just being an image.)

I suppose it could look for fleshtone colors or something; perhaps over a certain % of total, or if the fleshtoned pixels are "bunched up" in certain blobs of areas or something.

[pipeline_tux]

Yep, that's pretty much how they work. I can't find the details of it now, but the "smart" ones also do some colour transformations on the image so detection will work irrespective of what race the people in the porn are.