Data preparation In order to conduct our experiments and draw conclusions with strict control of variables , we collected 1856 ID photos that satisfy the following criteria Chinese , male , between ages of 18 and 55 , no facial hair , no facial scars or other markings , and denote this data set by S . Set S is divided into two subsets Sn and Sc for noncriminals and criminals , respectively . Subset Sn contains ID photos of 1126 noncriminals that are acquired from Internet using the web spider tool they are from a wide gamut of professions and social status , including waiters , construction workers , taxi and truck drivers , real estate agents , doctors , lawyers and professors roughly half of the individuals in subset Sn have university degrees . Subset Sc contains ID photos of 730 criminals , of which 330 are published as wanted suspects by the ministry of public security of China and by the departments of public security for the provinces of Guangdong , Jiangsu , Liaoning , etc . the others are provided by a city police department in China under a confidentiality agreement . We stress that the criminal face images in Sc are normal ID photos not police mugshots . Out of the 730 criminals 235 committed violent crimes including murder , rape , assault , kidnap and robbery the remaining 536 are convicted of nonviolent crimes , such as theft , fraud , abuse of trust corruption , forgery and rack eteering . Some sample ID photos in Sc and Sn are dis played in Figure 1 . The individuals in Sc and Sn are resi dents of a very large geographical areas , stretching from the northeast all the way to the far south of China and including poor and very rich provinces of the country . In all selected ID photos , only the region of the face and upper neck is extracted and the background is removed . All the extracted faces are normalized in size and aligned into an 80 80 image . Although all test face images are ID photos acquired with uniform frontal lighting , we still take extra measures to neutralize any possible effects of varied illumination conditions . Only the luminance component of all color face images is used to factor out the spectrum of the lighting and the skin color . Moreover , all resulting grey scale images are normalized to have the same intensity dis tribution or the same overall tone production . This is done by matching the histogram of every input image to the aver age histogram for the entire data set of 1856 grey scale face images . All ID photos in S are JPEG compressed with QP factor of 90 or higher . Still we applied JPEG soft decoding tech niques 23 , 28 to remove small perceptually transparent compression noises in the process any devicedependent , signallevel signatures are destroyed as well .