1. A method for determining if an image of a face is a face candidate, where a face rectangle is defined as {x f ,y f ,h f ,w f }, where {x f ,y f } are the coordinates of a left top point, {h f ,w f } are the height and width of the face rectangle, respectively, left and right eyes of the face are defined as {x le ,y le ,h le ,w le } and {x re ,y re ,h re ,w re } respectively, with {x le ,y le }, {x re ,y re } being left top points of the coordinates of the left and right eyes, respectively, and {h le ,w le }, {h re ,w re } being the height and width of the left and right eyes, respectively, and {h I ,w I } denotes the height and width of the image, respectively, comprising: capturing an image of a face with an image capture device; and using a processor to determine if the face is a face candidate by examining the face for the following criteria: (1) the face should appear in the middle of the image, such that x f ≧θ l ×w I , x f +w f ≦θ r ×w I , y f ≦θ t ×h I , y f +h f ≦θ b ×h I , where 0≦θ l , θ r , θ t , θ b ≦1 and θ l , θ r , θ t , θ b are four pre-defined thresholds; (2) the face should be sufficiently large, such that min(h f ,w f )≧θ s ×min(h I ,w I ), θ s is a pre-defined threshold; (3) the left and right eyes should be located in a horizontal line, such that |y le −y re |≦max(min(h le ,h re )×γ 1 ,3) where γ 1 is a pre-defined threshold; (4) the left and right eyes should have similar size, such that |w le −w re |≦max(min(w le ,w re )×γ 2 ,3), where γ 2 is a pre-defined threshold; (5) a distance between the left and eyes should be within a range, such that w f ×γ 3 <|x lc c −x rc c |<w f ×γ 4 , where x lc c , x rc c are x-coordinates of the left and right eye rectangle center points, respectively, and γ 3 and γ 4 are pre-defined thresholds; (6) a size of the left and right eyes should be within a range, i.e., min(w le ,w re )≧w f ×γ 5 , max(w le ,w re )≦w f ×γ 6 , where γ 5 and γ 6 are pre-defined thresholds; and (7) the left and right eyes should be located in the middle of the face, i.e., x f +w f −x re −w re ≧w re ×γ 7 , x le −x f ≧w le ×γ 8 , where γ 7 and γ 8 are pre-defined thresholds; and outputs to an output device a result that the image of a face is a face candidate when the criteria (1) through (7) are met.