1. An iris registration method, comprising: a first step of capturing, by a capture device, a plurality of iris images of an iris of a person to be registered and storing the plurality of iris images in a computer-readable recording medium; a second step of generating features from the respective iris images obtained in the first step; a third step of selecting from the features obtained in the second step a predetermined number of registration features, using authentication performance as an evaluation index and storing the predetermined number of registration features in a computer-readable recording medium; and a fourth step of setting a distribution of the number of iris images with respect to pupil diameter/iris diameter ratio, acquired under a condition that the person to be registered performs authentication, wherein in the third step, a predetermined evaluation value indicating authentication performance is calculated by using a weight according to the number of features in each pupil diameter/iris diameter ratio and taking the distribution set in the fourth step into consideration, and the registration features are selected using the thus calculated evaluation value wherein the second step, the third step, and the fourth step are embodied as computer executable instructions and are executed by a processor.