An image processing apparatus includes: a holding unit that holds a plurality of images; a condition checking unit that checks imaging conditions of the plurality of images; a collation determining unit that determines whether to collate images among the plurality of images based on the imaging conditions of the images; a collation unit that collates the images determined to be collated by the collation determining unit to obtain a degree of similarity; and a classifying unit that classifies the collated images into a same category when the degree of similarity is equal to or greater than a predetermined threshold.