1. An image processing device, comprising: an input unit that inputs an image obtained by imaging; a resize processing unit that performs one of enlargement and reduction processing for the image input by the input unit as a category decision target image, so as to obtain a first image equivalent of a predetermined camera-to-subject distance; a feature amount calculation unit that calculates a first feature amount that indicates a feature of the first image resized by the resize processing unit; and a decision unit that makes a category decision on the category decision target image based upon the first feature amount, the category decision being to make a decision as to which of a plurality of categories the category target image corresponds to.