Related:

http://blog.vjeux.com/2012/image/best-cropping-position.html

http://seatgeek.com/blog/dev/opencv-face-detection-for-cropp...

https://github.com/globocom/thumbor

It's definitely an open question for me. That's probably why the Desktop Newsfeed has such inconsistent cropping – because it's trying to center the face.

I'd love to hear that from the Photo Team, though.