1. An image processing apparatus comprising: an identification unit configured to identify a main subject region and a background region different from the main subject region with respect to a plurality of images captured by an image capturing unit; a composition unit configured to align the main subject regions of the plurality of images and to generate a composite image in which predetermined blur processing is applied to the background region; a detection unit configured to detect an amount of movement of the background region between the plurality of images; and a control unit configured to control an amount of blurring in the blur processing based on the amount of movement of the background region between the plurality of images detected by the detection unit.