How to do face detection from a video for face recognition

how should i do face detection from a video such that i can perform PCA for face recognition.The code i used for detection performs well but at the recognition phase i get same image for all the detected faces because there is very less difference in the pixel values of the detected faces.

Answer 1

[Image Analyst]

See how Brett Shoelson of the Mathwork does it with the app on his File Exchange: http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A911