1. An image processing apparatus comprising: an extraction unit configured to extract a structure of a tested eye from an OCT image obtained by optical coherence tomography, and configured to extract a structure of the tested eye from an eyeground image obtained by a scanning laser ophthalmoscope or a fundus camera; a calculation unit configured to calculate a reliability degree of the extraction for each of the structure extracted from the OCT image and the structure extracted from the eyeground image based on comparison of the structure extracted from the OCT image and the structure extracted from the eyeground image; and a display control unit configured to display each of the structure extracted from the OCT image and the structure extracted from the eyeground image superimposed on the eyeground image in display patterns according to the calculated reliability degree.