An authentication device includes: a memory; and a processor coupled to the memory and configured to: acquire a plurality of images with regard to a certain living body, extract first biometric information from each of the plurality of images, perform an alignment between the plurality of images, based on the first biometric information, calculate a coefficient based on feature of the certain living body, the feature being identified by a result of the alignment, and generate a normalized image by normalizing at least one image from among the plurality of images based on the coefficient.