1. An image processing apparatus used to specify an abnormal part of a subject, comprising: a calculation unit configured to calculate position adjustment data used for matching between contour data of a specific subject which have been extracted from an X-ray radiographic image and contour data of a photographic image obtained by photographing the specific subject; and a display processing unit configured to display a three-dimensional X-ray CT image which has been correlated with the X-ray radiographic image and a two-dimensional biolight image which has been correlated with the photographic image in superposition by using the calculated position adjustment data.