Algorithm to detect photo orientation

Question

I would like to rotate photos automatically, even when EXIF metadata about the image orientation is not available.

Are there any good algorithms for detecting the or

Answer 1

I could only find http://sourceforge.net/projects/rotator/.

I used a test set of holiday photos comprising 70 pictures with about 18 requiring rotation.

After processing with the default settings, there were 20 that were either rotated or not rotated in error.

Not so great a result.