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Countermeasures
Photonic and spectrographic countermeasures
- spectrographic properties of tissue, fat, and blood
Diferent components of living tissue have distinctive spectrographic signatures. Comparing the fractions of light reflected in 600nm - 1000nm band can reveal these.
- spectrographic properties of melanin pigment
The pigment present both in human skin and in the anterior layer of the iris, called melanin, has a distinctive absorption spectrum peaking at 350nm, with little infrared absorption.
- coaxial retinal back-reflection (red eye" efect)
A light source that is imaged as a focused spot on the retina is re-imaged by the optics of the eye as an outward-going parallel beam, from the pupil back to the original source. If a camera is nearly on-axis with that source, the pupil of the eye appears bright, and red because of the retina. This effect confirms the "eye" has functional cavity optics.
- 4 Purkinje refections from corneal and lens surfaces
A natural human eye has four optical surfaces, each of which reflects bright lights: the front and back of the cornea, and the front and back of the lens. (Three are curved outward, and one is curved inward.) The positions of these 4 Purkinje reflections depend on the geometry of the light sources. A real eye must track them dynamically, and correctly.
Behavioural countermeasures
- involuntary: autonomic nervous system
- hippus (pupillary unrest)
- pupillary light reflex (brainstem control)
- voluntary: conscious control, challenge responses
- eye movements on command
- eyelid blinks on command
Tracking the pupil boundary, the iris boundary, and both
eyelids boundaries, enables all of these dynamic liveness tests.
Detection of fake iris pattern printed onto a contact lens
