1. An image processing apparatus, comprising: a fundus image acquiring unit configured to acquire a fundus image of an eye to be inspected; a designating unit configured to designate at least two arbitrary points on the fundus image; a tomographic image acquiring unit configured to acquire a tomographic image of the eye to be inspected; a deviation amount calculating unit configured to calculate a deviation amount between a distance between a first arbitrary point and a second arbitrary point of the at least two arbitrary points on the fundus image, and a distance, measured along a retina on the tomographic image, between a first point and a second point on the tomographic image, wherein the first point and the second point correspond to the first arbitrary point and the second arbitrary point respectively; and a converting unit configured to convert the tomographic image on the basis of the deviation amount so that the first and second arbitrary points on the fundus image match with corresponding points on the tomographic image.