The authors would like to thank to Kah-Kay Sung and Dr. Tomaso Poggio (at MIT) and Dr. Woodward Yang (at Harvard) for providing a series of test images and a mug-shot database, respectively. Michael Smith (at CMU) provided some digitized television images for testing purposes. We also thank Eugene Fink, Xue-Mei Wang, Hao-Chi Wong, Tim Rowley, and Kaari Flagstad for comments on drafts of this paper.