algorithms for automatically cropping?

IM wizards,

My question is not directly an IM question, but relates to algorithms
/ techniques for automatically cropping images ...

I need to crop a bunch of photos to square while creating thumbnails.
I am currently using ImageMagick to crop the largest square from the
center of the photo ... works fine.

I am wondering if there are algorithms that could do a better job of
identifying the more interesting parts of a photo (like simple face
detection) or eliminating relatively uninteresting parts of a photo
(like blue sky or white walls).

Doesn't have to be perfect. I am just looking for a simple improvement
over grabbing the square from the center of the photo.

Any feedback / advice / experiences would be appreciated.


Michael