1. A feature point location determination method comprising: the following steps and using a processor to perform one or more of said steps: a first search step of searching for locations of a plurality of feature points in a predetermined first search area in an image; a location correction step of correcting the locations of the plurality of feature points based on a geometric layout relationship among the plurality of feature points searched for by in said first search step; a second search step of setting a second search area based on the locations of the plurality of feature points corrected by in said location correction step and searching for locations of the feature points in the second search area; a reliability calculation step of calculating reliability of each of the feature points searched for from the second search area based on reliability distribution in the second search area; a distance calculation step of calculating distance between the locations of each of the feature points before and after correction in said location correction step; a determination step of determining a threshold based on the distance calculated in said distance calculation step; and a selection step of selecting one of the location corrected in said location correction step and the location searched for in said second search step, as the location of each of the feature points to be localized, based on a comparison result between the reliability calculated in said reliability calculation step and the threshold determined in said determination step.