1. A method of detecting an object through a retrieve of an image representing an object matched to an object represented by a query image from an image database that includes a plurality of reference images and is created by extracting a plurality of reference feature vectors from each reference image that represents an object, each of the reference feature vectors representing a feature of one of local areas in each reference image, and by storing the reference feature vectors in such a manner that each of the reference feature vectors is associated with the corresponding reference image and with an object ID that identifies the object represented by each reference image, the method comprising the steps of: extracting a plurality of vectors from the query image as query feature vectors, each of the query feature vectors representing a feature of one of local areas in the query image; comparing each query feature vector with each reference feature vector, and calculating a similarity score that is determined to have a greater value in case where the query feature vector and the reference feature vector are closer, in case where a local area from which the query feature vector is extracted is greater, and in case where a local area from which the reference feature vector is extracted is greater; determining a reference feature vector which provides the highest similarity score as a similar vector for each query feature vector; and obtaining resulting scores through a predetermined calculation procedure according to the respective object IDs, each object ID being associated with the similar vector, and determining, as a detection result, at least one object that is specified by an object ID giving the highest resulting score, wherein each resulting score is calculated according to the following equation: [ Equation 1 ] s = ∑ s f N f ( 1 ) wherein s f is the similarity score regarding the similar vector, and N f is a number of query feature vectors each of which matches to a reference feature vector originated from a reference image representing an object regarding the object ID and being stored in the image database out of the query feature vectors in the query image.