1. An image processing apparatus comprising: a region detection section configured to detect a candidate region in which a structure having a predetermined shape is estimated to exist, from an image obtained by image-pickup of a living tissue; a border pixel detection section configured to detect a border pixel corresponding to a border of the candidate region; a region setting section configured to set at least one local region having an area for one or more pixels in each of two neighboring regions located in the vicinity of and both sides of the border pixel; a feature value calculation section configured to calculate predetermined feature values based on predetermined values obtained for respective pixel units in the respective local regions set by the region setting section; a discrimination value calculation section configured to calculate, based on a calculation result of the predetermined feature values in a first local region group set in the neighboring region located on one side when viewed from the border pixel and a calculation result of the predetermined feature values in a second local region group set in the neighboring region located on the other side when viewed from the border pixel, a discrimination value for allowing a difference in the two calculation results of the predetermined feature values to be discriminated; and a candidate region correction section configured to correct a detection result of the candidate region obtained by the region detection section, based on a calculation result of the discrimination value.