1. An apparatus for recognizing a head region in a CT lateral image of a subject, comprising: a deriving unit for deriving a first image representing a bone of the subject from the CT lateral image; an extracting unit for extracting a boundary curve indicating an outer contour of a region comprising at least part of the occipital bone and at least part of the cervical vertebra of the subject in the first image; and a determining unit for determining a first pixel position indicating a bottommost point of the head region of the subject, based on a shape feature parameter of the boundary curve.