1. An image processing apparatus, comprising: an input data obtaining section for obtaining input image data; a features extracting section for extracting features of the input image data; a storage control section for causing identification information for identifying a reference image to be stored in a storage section in such a manner that the identification information is related to features of the reference image; a similarity determination section for comparing the features of the input image data with features of a least one reference image stored in the storage section, so as to determine a similarity between an input image and the at least one reference image; an instruction input section for receiving an instruction input by a user; and a display section for displaying information, the storage control section dividing a storage region of the storage section into a plurality of divided regions, the storage control section causing each of the plurality of divided regions to be related to a storage condition under which the identification information for the at least one reference image is to be stored in said each of the plurality of divided regions, and when causing the identification information to be stored in the storage section, the storage control section selecting a storage region where the identification information is to be stored, out of the plurality of divided regions in accordance with the storage condition, and the storage control section causing, in a case where a plurality of reference images have common features, a plural pieces of identification information for identifying the respective plurality of reference images to be stored in the storage section in such a manner that the plural pieces of identification information are related to each one of the common features of the plurality of reference images, the instruction input section receiving a selection instruction to select a divided region where the at least one reference image whose similarity to an input image is to be determined is stored, or an instruction regarding a storage condition for the at least one reference image whose similarity to an input image is to be determined, the storage control section causing the similarity determination section to determine a similarity between the input image and the at least one reference image whose features and identification information are stored in a divided region corresponding to the selection instruction received by the instruction input section, or in a divided region corresponding to the storage condition received by the instruction input section, the storage control section causing the display section to display a thumbnail image of each of the at least one reference image or a list of the at least one reference image that is determined by the similarity determination section as being similar to the input image, and the storage control section deleting, from a corresponding one of the plurality of divided regions, identification information of the at least one reference image selected by the user via the instruction input out of the thumbnail image of each of the at least one reference image or the list of the at least one reference image displayed by the display section.