1. Recent Advances in Optical Image Processing
2. Elimination of redundant operations for a fast Sobel operator
3. Rapid object detection using a boosted cascade of simple features;Viola,2001
4. http://docs.opencv.org/trunk/d7/d8b/tutorial_py_face_detection.html
5. Face Detection using LBP features, Jo Chang-yeon, CS 229 Final Project Report, December 12, 2008