I was enjoying playing photofunia.com a while ago when I got interested on how I can implement such a thing with opensource tools, specifically LAMP. In less than a minute, with “php face detection” on Google I found this.

The headline does say face detection – but what does this mean? Easy said, this article focus on how to find faces on images with PHP. Faces have a certain form and so it is possible to search for it. At the end of the search you will say how many human faces are on the image or better: Where are human faces on my image. This article is not intended to be mathematically.

Intel works on the OpenCV library to search for structures on images. The library is shipped with training files, what was trained with hundrets of photos to detect faces from different perspectives on images and so we can focus on the PHP part.

http://www.xarg.org/2008/07/face-detection-with-php/