1. An image processing apparatus for processing an image, comprising: a face detector that detects a face image of a subject contained in a captured image based on image information of the captured image supplied from an imaging unit; a face feature detector that detects a face feature contained in the face image based on image information of the face image detected by the face detector; a normalizer that normalizes the face image detected by the face detector based on a detected position of the face feature detected by the face feature detector, generates a normalized face image, and measures a normalization score corresponding to the normalized face image; a face expression detector that detects a face expression contained in the face image based on image information of the normalized face image generated by the normalizer; and a photographing controller that determines whether a normalization operation of the face image has been successfully completed based on the normalization score measured by the normalizer, and instructs the imaging unit to perform a photographing operation in response to the face expression detected by the face expression detector only if it is determined that the normalization operation of the face image has been successfully completed.