This web site answers one simple question: Is the person in that picture naked?
It sounds like a joke, but it was created by a company called Algorithmia to demonstrate how complicated math and photo detection techniques can automatically filter out images that are not okay to post on more family-friendly websites.
Basically, Algorithmia writes in a blog entry, IsItNude.com scans for faces, and tries to match the skin tone of a subject's nose to any other portion of a picture. If there's a match, it means the subject probably isn't wearing a shirt, and it gets returned as nude.
And just like Microsoft's How-Old.Net, it gets smarter and better at guessing over time, thanks to the application of what developers call "machine learning."