Face detection is a simple technique to highlight a face in a photograph.You might have used automatic face detection in Picasa web albums that can be easily done using the PHP script.
Face detection is a computer technology that determines the locations and sizes of human faces in arbitrary (digital) images. It detects facial features and ignores anything else, such as buildings, trees and bodies.
Face detection is actually a pattern matching technique,Open CV a opensource face detection library created by inter can be used to face detection.
Without Open CV you can apply face detection using the PHP class mentioned at this blog
$detector = new Face_Detector('detection.dat'); $detector->face_detect('your_file.jpg'); $detector->toJpeg();
download the script here.