1. An apparatus for processing a depth image, the apparatus comprising: a depth image obtainer to obtain a depth image; an object image extractor to extract an object image from the depth image; a relative angle calculator to calculate a relative angle between an image sensor used to photograph the depth image and a target object corresponding to the object image; and an object image rotator to rotate the object image based on the relative angle and a reference angle, the reference angle being related to reference images prepared in advance to recognize the object image.