[racbart]

Wouldn't testing for skin colors produce far too many false positives to be useful? All these beach photos, fashion lingerie photos, even close portraits. And how about half of music stars these days who seem to try to never get caught more clothed than half naked?

Nudity != porn and certainly half-nudity != porn.

I'd rather go for pattern recognition. There's lot of image recognition software these days that can distinguish the Eiffel Tower from the Statue of Liberty and it might be useful to detect certain body parts and certain body configurations (for these shots that don't contain any private body part but there are two bodies in an unambiguous configuration).

[betterunix]

"detect certain body parts"

When I was a kid, we had a firewall at school that tried to filter pornography by doing something similar with text. Doing research on breast cancer turned out to be rather tricky.

So let's say you try to detect certain body parts. Now you have someone who wants to know more about their body, but you are classifying images from medical / health articles as pornography.

"certain body configurations"

So now instead of having trouble reading about my own body, I will have trouble looking at certain martial arts photos:

https://upload.wikimedia.org/wikipedia/commons/1/14/BostonKe...

I am not saying these are unsolvable problems, but they are certainly hard problems. Even using humans to filter images tends to result in outrageous false positives sometimes:

http://abcnews.go.com/Health/breastfeeding-advocates-hold-fa...

[racbart]

You are correct and I'm not saying that I described the Holy Grail of detecting porn in a single paragraph. I'm just pointing to another direction. No solution to a very complex problem could be one-dimensional. Combining several different tests might lead to a solution. I.e. these jujitsu photos should not even be detected as “certain body configurations” as people there are fully clothed and there's not much actual bodies seen in the picture (so mentioned skin color definitely should come to play when detecting wether you see a body or not).

At the end of the day I doubt there could be a fully bulletproof and always correct solution using current state of tech. But you need to factor much more than just skin color if you try to build an automated solution to this problem.

[icebraining]

There's plenty of fully clothed porn out there. They're even tags on some porn sites.

[ElliotH]

When I was in a boarding college we had wardrobe doors that were the perfect colour to set off the skin-tone filters.