An image processing apparatus includes a processing unit configured to perform, on a luminance distribution acquired in at least one direction crossing a vessel region in a fundus image of a subjects eye, a first smoothing operation for each first size and a second smoothing operation for each second size smaller than the first size a first identifying unit configured to identify a position of a vascular wall in the fundus image on the basis of the luminance distribution obtained by performing the first smoothing operation and a second identifying unit configured to identify positions of inner and outer boundaries of the vascular wall in the fundus image on the basis of the luminance distribution obtained by performing the second smoothing operation.
