1. An apparatus for detecting a face in an image using classifiers generated by a boost algorithm, the apparatus comprising: an image dividing unit dividing a black and white image into sub-windows; a sub-window detection unit detecting a sub-window corresponding to a face image in the divided sub-windows using only a front part of a cascade of the classifiers and storing the sub-window detected as the face image; and a post-processing unit verifying whether each of sub-windows included in a group selected in response to the number of child detections in each group among a plurality of groups into which stored sub-windows are grouped is the face image using a latter part of the cascade of the classifiers and a plurality of thresholds which are proportional to a size of the sub-window and are less than the average number of child detections, integrating the sub-windows in the group according to the result of the verification, and outputting the result of the integration as the face image included in the black and white image, wherein the number of child detections is the number of sub-windows included in a group.