1. An estimation method executed by a computer, the estimation method comprising: extracting, from an image, a plurality of characteristic points satisfying a certain requirement regarding changes in gray levels between the plurality of characteristic points and surrounding points; identifying, as map points from the plurality of characteristic points, characteristic points existing on planes, by excluding corners of an object depicted on the image; extracting, from another image, another plurality of characteristic points satisfying the certain requirement; executing matching of the another plurality of characteristic points with the map points based on a region including the map points; and estimating, based on results of the matching, a position and an orientation of an imaging device while the another image is captured.