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 vector calculating unit configured to calculate a vector formed between first and second of the at least two arbitrary points; a coordinate calculating unit configured to calculate a coordinate system with the vector being set as one axis and the first arbitrary point being set as an origin; a tomographic image acquiring unit configured to acquire a tomographic image of the eye to be inspected; a determining unit configured to determine a point on the tomographic image that corresponds to the first arbitrary point in the fundus image; a deviation amount calculating unit configured to calculate a deviation amount between a position of the second arbitrary point on the fundus image and a position of a corresponding point on the tomographic image; 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.