An image of the iris contained in an image of an eye is accurately specified. An image of the iris contained in a digital image (P) of an eye is accurately specified. In view of low-intensity pixels of the digital image (P) of the eye, and high-intensity pixels having a predetermined relationship with the low-intensity pixels, a reference pixel (PX0) that defines the center of the pupil is determined. Thereby, the center of the pupil can be specified more accurately when compared to the case where, for example, it is determined only from the low-intensity pixels. Therefore, the accuracy of the process to specify the iris image on the basis of the reference pixel is improved, and as a result, the iris image can be accurately specified.
