Today I spoke with someone who's an expert in computer vision. I didn't know anything about the state of that field, but one thing he told me was that computers can detect, with a high degree of accuracy, whether a figure they "see" is a woman or a man.
The two primary determinants are the length of the person's hair and the amount of skin exposed. Women have more of both, generally.
So the types of men that can trip up computer vision on this problem are men with long hair who show lots of flesh. So I'm thinking common false positives include Axl Rose, Fabio, and some members of the Hell's Angels?