Hyun Joo So Mi Hye Kim Yun Su Chung Nam Chul Kim Face Detection Using Sketch Operators and Vertical Symmetry. 541-551 2006 conf/fqas/2006 FQAS http://dx.doi.org/10.1007/11766254_46 db/conf/fqas/fqas2006.html#SoKCK06