An image processing method is for processing image data that has been captured by an image sensing apparatus having an image sensing device in which a plurality of photoelectric conversion elements are arrayed two-dimensionally for outputting an electric signal in accordance with an incident amount of light. According to the method, attitude information representing the attitude of the image sensing apparatus is input and, in a case where the input attitude information of the image sensing apparatus indicates an attitude that has been specified in advance, the image data is subjected to rotation processing, which conforms to the attitude specified in advance, successively in units of a prescribed number of pixels divided into a plurality of areas.