1. An image processing device that classifies a region of interest included in an image into multiple classification items, comprising: an initial region detector that detects at least part of the region of interest and sets the part as an initial region; an expansion region detector that detects an expansion region by expanding the initial region; and a region determining unit that calculates feature data of the initial region and the expansion region, and determines, based on the feature data, to which of the multiple classification items the region of interest belongs.