1. An iris recognition method, which considers pupil size variations due to changes in at least one intensity of lighting so as to enhance iris recognition accuracy, the iris recognition method comprising: obtaining multiple iris images having different pupil sizes by capturing iris images of a person to be enrolled with a camera installed in an iris recognition device while adjusting brightness of lighting so that the pupil size of the person to be enrolled varies from a maximum size to a minimum size, wherein the iris recognition device performs the iris recognition method and wherein the iris recognition device comprises the camera, a microprocessor, an iris enrollment database, and an iris recognition program; storing the obtained iris images and associated iris size information for enrollment in the iris enrollment database that is interworking with the iris recognition device; capturing an iris image for identification of a person to be identified with the camera installed in the iris recognition device; selecting enrolled iris images of each enrolled person from the iris enrollment database based on iris size information of the iris image captured for identification, and measuring a similarity between the iris image captured for identification and the selected enrolled iris images through comparison, wherein the iris size information of iris images for enrollment and the iris image for identification is determined according to an iris contraction ratio set {r(t)/R(t)} of values obtained by dividing an inner iris radius of a particular iris image by an outer iris radius of the particular iris image for an angle t in a given range; and performing authentication or identification of the person to be identified based on results of the similarity measurement between the captured iris image and the selected enrolled iris images.