16. An image processing method comprising: extracting a feature information from an object in input image data; classifying a plurality of feature information into a plurality of groups based upon a similarity, and registering the plurality of feature information into a dictionary, wherein the dictionary is used to determine a similarity between the feature information registered in the dictionary and the feature information extracted in the extracting; and deleting, among the plurality of groups, a feature information of a group, which does not reach a predetermined use level, from the dictionary, wherein a name of an identifier of the group which can be rewritten by a user is used as the use level, and wherein in the deleting, a group whose name of the identifier is an initial value is deleted from the dictionary, as the group not reaching the predetermined use level.
16. An image processing method comprising: extracting a feature information from an object in input image data; classifying a plurality of feature information into a plurality of groups based upon a similarity, and registering the plurality of feature information into a dictionary, wherein the dictionary is used to determine a similarity between the feature information registered in the dictionary and the feature information extracted in the extracting; and deleting, among the plurality of groups, a feature information of a group, which does not reach a predetermined use level, from the dictionary, wherein a name of an identifier of the group which can be rewritten by a user is used as the use level, and wherein in the deleting, a group whose name of the identifier is an initial value is deleted from the dictionary, as the group not reaching the predetermined use level. 19. The method according to claim 16 , wherein, in a case where the number of feature information registered in the dictionary exceeds a predetermined number, the feature information of a group which does not reach the predetermined use level is deleted from the dictionary.