Note this is designed to fool facial detection, not recognition. Detection generally uses much simpler algorithms because in most cases it needs to be orders of magnitude faster.

I was working on a project with OpenCV a few years ago. After a few embarrassing incidents I had to add a kludge whereby if it detected a small face directly above a big face, it was to discard the big one.

It turns out that the torsos of portly women with large breasts make ideal face candidates.