1. An image processing apparatus comprising: an image acquisition unit configured to acquire an image; a feature amount acquisition unit configured to set a plurality of partial regions for the image acquired by said image acquisition unit, and acquire an image feature amount including a plurality of frequency components from each of the partial regions; a holding unit configured to hold, as a background model, an image feature amount of an image as a background for each of the partial regions; a comparison unit configured to compare, for each of the partial regions, the image feature amount of the background model with the image feature amount acquired by said feature amount acquisition unit; an update unit configured to update, based on the comparison result of said comparison unit, each of a plurality of frequency components included in the image feature amount held in the background model using the image feature amount acquired by said feature amount acquisition unit by a degree according to each of the frequency components; and a detection unit configured to detect, using the background model updated by said update unit, for each of the partial regions, a region where a target object to be detected exists.