1. A method of normalizing a digital image of an iris of an eye of a vertebrate, including a human vertebrate, for the purpose of creating an iris code for use in the identification of the vertebrate, the method comprising the steps of: determining a pupil region in the image as a convex region having a boundary that can only be described by more than five independent parameters; determining, in the image, an outer boundary of the iris; and transforming an image of a ring shaped iris region that surrounds the pupil region into a coordinate system in which each point of the iris region is described by a first coordinate that indicates the position of the point along the boundary of the pupil and a second coordinate that indicates the distance of the point from said boundary, said second coordinate having a constant value when the point is located on the outer boundary of the iris.