check this out! http://digg.com/programming/Automatic_Face_Detection_in_Photos_with_PHP Its pretty interesting
Very interesting indeed. The only problem is getting your hosting provider to install OpenCV and PHP module. Most of the time you won't success. Unless you have a dedicated server with root account, of course.
Thanks, I'll test it when I have more free time. Here is another solution for face detection without using external libraries. It's written in pure PHP and is suitable for applications when you don't have dedicated server: http://svay.com/blog/index/post/2009/06/19/Face-detection-in-pure-PHP-(without-OpenCV)