1. A method of detecting a varied region comprising: receiving, by a processor, a captured image captured by an imaging device; selecting, by a processor, first characteristic points to be used for calculation of a geometric transformation parameter, from characteristic points in the captured image and characteristic points in a reference image; calculating, by a processor, the geometric transformation parameter based on the selected first characteristic points; selecting, by a processor, second characteristic points to be used for determination of a similarity between the captured image and the reference image, from the characteristic points in the captured image and the characteristic points in the reference image; performing, by a processor, geometric transformation on the selected second characteristic points based on the calculated geometric transformation parameter; calculating, by a processor, the similarity between the second characteristic points in the captured image and the second characteristic points in the reference image, after the geometric transformation; identifying, by a processor, a varied region based on the determined similarity, wherein the performing the geometric transformation performs the geometric transformation on the second characteristic points in the captured image to obtain the transformed second characteristic points, searches for a closest characteristic point in the reference image, the closest characteristic point being closest to each of the transformed second characteristic points, calculates a distance between each transformed second characteristic point and the closest characteristic point corresponding to the transformed second characteristic point, and compares the calculated distance with a predetermined threshold, and the identifying the varied region divides the captured image into a plurality of local regions, calculates a number of the second characteristic points having the distance larger than the predetermined threshold in each local region, and identifies a local region in which the calculated number of the second characteristic points is larger than a predetermined number, as the varied region.