1. An image processor comprising: a general-purpose classifier configured to detect a predetermined large classification target, the general-purpose classifier including one or a plurality of weak classifiers in which a next-stage weak classifier performs detection processing to a preceding-stage output domain; and a dedicated classifier configured to detect a small classification target which is a subdivision of the large classification target, the dedicated classifier including one or a plurality of weak classifiers in which a next-stage weak classifier performs the detection processing to the preceding-stage output domain; wherein the image processor comprises: an image acquisition part configured to acquire a photographed image photographed by a camera; an image extracting part configured to extract a registered image including a domain assigned by a user from the photographed image; a dedicated classifier performing part configured to cause the dedicated classifier to perform the detection processing to the registered image extracted by the image extracting part; a dedicated classifier selector configured to select the dedicated Classifier having a highest index indicating superiority or inferiority of a detection result; and a classifier generator configured to generate a registered image classifier to detect a target included in the registered image by replacing some weak classifiers included in the dedicated classifier selected by the dedicated classifier selector with the weak classifiers included in the general-purpose classifier.