I've written the cropping algorithm being used at Facebook, here is a write-up of the method if you are interested: http://blog.vjeux.com/2012/facebook/best-cropping-position.h...

I tried to use saliency-based approaches but they don't really work that well for non artistic photos. For example, this image[1] would have edges everywhere but next to the faces.

If you have some time, I would be interested in seeing the results of your approach in my example images[2].

[1] - https://fbcdn-sphotos-c-a.akamaihd.net/hphotos-ak-snc6/p206x...

[2] - http://blog.vjeux.com/wp-content/uploads/2012/10/cropping.ht...