1. An image processing apparatus comprising: an image input section via which a medical image picked up of a mucous surface of a living body, the medical image including a plurality of pixels, is inputted; a setting section that sets a region of interest as a first region including one or more pixels in the medical image and sets a second region including a unit region including the one or more pixels that are different from those of the region of interest in the medical image; a feature value calculating section that calculates a first feature value relating to a shape of the region of interest based on a pixel value of the region of interest set by the setting section and a pixel value of a region in a periphery of the region of interest, and calculates a second feature value relating to a shape of the unit region based on a pixel value of the unit region and a pixel value of a region in a periphery of the unit region; and a matching section that matches the region of interest with a predetermined shape based on distributions of the first feature value and the second feature value calculated by the feature value calculating section.