1. An image processing apparatus for processing an image acquired by imaging a living body, the image processing apparatus comprising: a blood vessel candidate region extraction unit configured to extract a plurality of blood vessel candidate regions from the image; an identical blood vessel candidate region extraction unit configured to 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; an evaluation value calculation unit configured to 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; and a blood vessel region discrimination unit configured to discriminate whether or not the identical blood vessel candidate region forms an identical blood vessel region, based on the evaluation values.