1. An image processing apparatus comprising: a processor; and a memory storing computer-readable instructions that, when executed by the processor, implement: an area extracting unit that extracts a candidate area of a classification target area in which a pixel value does not correspond to a three-dimensional shape of an imaging target based on pixel values of an intraluminal image acquired by imaging the inside of a lumen or information of a change in pixel values of peripheral pixels; and an area classifying unit that classifies the candidate area as the classification target area based on the pixel values of the inside of the candidate area, a boundary portion of the candidate area, or a periphery portion of the candidate area.