nude.js (http://www.patrick-wied.at/static/nudejs/) is a Javascript library that detects nudity in images.
I can't attest to its effectiveness but it maybe what you're looking for.
I can't attest to its effectiveness but it maybe what you're looking for.
Reading through the link, I believe it does a combination of skin tone detection and human body pattern matching. Typically, this solution can detect a fully nude human pretty well, but fails on something like a close-up/partial shot of a penis.