1. An identification device that performs identification according to a face area contained in image data, comprising: a feature data extraction unit configured to extract feature data from a face area in each of a plurality of frames of image data, as extracted feature data; a storage unit configured to register therein feature data for use in the identification; an identification unit configured to perform identification through comparison between the feature data registered in said storage unit and the extracted feature data, and to identify the extracted feature data and the feature data registered in said storage unit as being associated with an identical person or individual when a difference between the extracted feature data and the feature data registered in said storage unit is smaller than a second threshold value which is smaller than a first threshold value; a tracking unit configured to identify an identical face area in consecutive ones of the frames; and a registration unit configured to be operable when said identification unit identifies a face area in a first frame as one of the frames, but said identification unit does not identify a face area in a second frame following the first frame, which is identified by said tracking unit as identical to the identified face area in the first frame, and when said identification unit determines that the difference is larger than the first threshold value in the second frame, to register the extracted feature data associated with the face area in the second frame, as additional feature data, in said storage unit.