1. An image processing apparatus comprising a processor and a memory storing a background model generated from a background image, the background model including a feature of each region in the background image and stability in terms of time for the feature extracted from that region, and storing instructions which, when executed by the processor, cause the image processing apparatus to: input a video; divide an input image in the video into a plurality of regions based on superpixels; extract a feature from each of the plurality of regions; select with respect to a region of interest in the input image, based on the stability of the feature of each region in the background model, a neighboring region in the background model in a neighborhood of the region of interest; compare the feature extracted from the region of interest in the input image with a feature of the selected neighboring region in the background model; and determine for each of the plurality of regions in the input image whether the region is the background based on a result of the comparison.