Another method used to successfully spoof some iris sensors is to use a contact lens on which an
iris pattern is printed [42]. Even more sophisticated, multilayered and three-dimensional artificial
irises may also be produced to spoof a sensor [43].
Iris spoof detection may be accomplished in a variety of ways. Mathematical interrogation of the fine
texture of the iris image using Fourier analysis may be employed to detect and discriminate against
the dot matrix pattern of many common printing processes [44]. Fig. 2 shows images of a real and
fake iris and their associated Fourier spectrum. The unique optical effects of the iris and/or other
parts of the eye may be analyzed [45]. Involuntary motions of the pupil at rest (“hippus”) or in
reaction to changing ambient light conditions may be checked to determine if a live eye is in the
sensor’s field of view [46]. In addition, challenge-response transactions may be implemented
wherein the person under test is asked to blink or move their eyes in a certain direction to ensure
that the random instructions are carried out properly [47].