1. An apparatus comprising: an extraction unit configured to extract feature information from an object of image data; a registration unit configured to register, in a dictionary, the feature information extracted by said extraction unit; and a similarity determination unit configured to refer to the dictionary and determine a similarity between feature information registered in the dictionary and the feature information extracted by said extraction unit, wherein, of feature information to be registered in the dictionary, feature information not satisfying a predetermined evaluation criterion is not used in determination by said similarity determination unit.