1. An apparatus comprising: one or more processors; a memory storing a program to be executed by the one or more processors, wherein the program causes the one or more processors to execute; converting input image data to a bitmap data format; extracting feature information of an object of interest in the input image data from the input image data of the bitmap data format; referring to a dictionary and determining a similarity between feature information of an object registered in the dictionary and the feature information of the object of interest extracted from the input image data, wherein, in the dictionary, feature information of a plurality of objects are stored, each feature information is classified into one of a plurality of object-groups based on the similarity, and each feature information is associated with the image data in which an object represented by the feature information is included; registering, in the dictionary, the feature information of the object of the interest extracted from the input image data; determining whether a number of common images between an object-group of interest in the plurality of object-groups and object-groups other than the object-group of interest satisfy a predetermined criterion; and if the number of common images does not satisfy the predetermined criterion, updating the dictionary so that the feature information included in the object-group of interest is unusable when the dictionary is used for determining.