1. An image processing apparatus for processing an image acquired by imaging a living body, the image processing apparatus comprising: a processor comprising hardware, the processor being configured to: extract a plurality of blood vessel candidate regions from the image; extract, from among the plurality of blood vessel candidate regions, a blood vessel candidate region group estimated to form a line shape when integrated, as an identical blood vessel candidate region; calculate one or more kinds of evaluation values for evaluating a likelihood that the identical blood vessel candidate region corresponds to an identical blood vessel; discriminate whether or not the identical blood vessel candidate region forms an identical blood vessel region, based on the evaluation values; calculate depth information that is information corresponding to a distance between an imaging unit and a subject when capturing the image; and calculate feature data representing continuity of the depth information within the identical blood vessel candidate region, wherein the feature data representing the continuity of the depth information is used as the evaluation value.