It is established that the iris of a person is characteristic and equipment is available for deriving recognition parameters from an image of an iris. Iris recognition (1001) is reliable provided that the test object is an eye but there is a danger of inappropriate results when test equipment is offered an object which is not an eye, e.g. a patterned contact lens. This invention performs supplementary tests (1000) adapted to distinguish between a real eye and an object purporting to be an eye. Supplementary tests include: (a) Illuminating the test object with polarised light and observing the orthogonal polarisation. A simple test measures the intensity of the orthogonal polarisation. A low intensity implies that the test object is not an eye. A more complicated test comprises forming an image with the orthogonal polarisation. A real eye gives a distinctive pattern similar to a Maltese cross. (b) Measuring the intensity of light returned along the direction of illumination. A low intensity implies that the test object is not an eye. (c) Projecting an image of a test pattern onto a test pattern onto a test object purporting to be an eye. The distortion of the image implies that the test object is not an eye.
