1. An image processing apparatus comprising: a first imaging unit configured to capture a wide-area image; a second imaging unit configured to capture a partial image corresponding to a part of the wide-area image; one or more memories storing instructions; and one or more processors that, when executing the instructions, causes the image processing apparatus to: extract a feature amount in each image region of a plurality of objects from the captured images; determine, based on the extracted feature amount, a type of a feature amount used for discriminating each of the plurality of objects and a resolution of an image used for extracting a feature amount of the determined type; control the imaging units to output an image at the determined resolution; detect image regions of the plurality of objects from the wide-area image captured by the first imaging unit; and control the extraction unit to extract a feature amount of the determined type in each image region of the plurality of objects output at the determined resolution from the partial image captured by the second imaging unit.