1. An image processing apparatus comprising: an obtaining unit configured to obtain three-dimensional image data and positions of a plurality of feature points in the three-dimensional image data; a designation unit configured to designate a designation point indicating a portion of interest in the three-dimensional image data; a selection unit configured to select, using information determined by a position of the designation point and the positions of the plurality of feature points, a feature point from the plurality of feature points; a generation unit configured to generate, from the three-dimensional image data, a cross section image on a plane determined based on the position of the designation point and a position of the selected feature point; and a display control unit configured to cause a display unit to display the generated cross section image.