1. An image processing apparatus for processing an image obtained by capturing inside of a lumen of a living body, the image processing apparatus comprising: a processor comprising hardware, wherein the processor is configured to: perform a contour edge region extracting process comprising extracting a contour edge region of an examination target from the image; perform an examination region setting process comprising setting an examination region in the image so as not to include the contour edge region; and perform an abnormal structure identifying process comprising identifying whether a microstructure of a surface of the examination target is abnormal, based on texture information of the examination region, wherein the examination region setting process comprises: performing a candidate region setting process comprising setting examination candidate regions in the image; and performing a region determining process comprising determining the examination region from the examination candidate regions, based on information on the contour edge region, and wherein the region determining process comprises: performing a contour edge region eliminating process comprising eliminating the contour edge region present in the examination candidate regions; and determining, as the examination region, an examination candidate region that remains after the contour edge region is eliminated by the contour edge region eliminating process.