Fingerprints, palm patterns, or the like, are widely used for person authentication. These patterns are skin ridge patterns wherein a part of the epidermal tissue is embedded in the roughness structure of the dermis, and accordingly, the patterns can be directly observed from the outside. That is to say, the aforementioned pattern essentially corresponds to the deep layer structure of the skin such as dermis or the like. The skin of the portion such as a palm, a sole, or the like, has a special structure wherein the epidermal structure corresponds to the structure of the dermis beneath the epidermal tissue, unlike the skin of other portions, leading to the physiological advantages such as high sensitivity of the touch sensory nerves of which ends are positioned in the deep layer of the skin to external stimulation, great toughness regarding friction, and so forth. Conventionally, the fingerprints have been used for person authentication since the fingerprints exhibit sufficient stability essentially due to the high stability of the deep layer structure therebeneath.
However, the aforementioned biometric authentication using the fingerprints does not provide sufficient security against so-called “spoofing” or the like. That is to say, the fingerprints are readily left on various objects, and the fingerprints left on the object can be easily observed, leading to a risk that other persons would forge the fingerprints.
On the other hand, it is expected that biometric authentication using the epidermal tissue of other portions avoids the aforementioned risk of forgery, for example. However, the epidermal tissue changes due to metabolism thereof in a 28-day cycle. Furthermore, the epidermal tissue readily exhibits various conditions due to rough skin, dry skin, or the like. Accordingly, the epidermal tissue of other portions does not have sufficient stability. Furthermore, it has become clear from measurement that the patterns of the epidermal tissue of the base portion of a finger, the thenar region, and the like, do not correspond to the patterns thereunderneath at all, rather, in some cases, the patterns of the epidermal tissue thereof are formed orthogonal to the patterns thereunderneath, except for a special case such as the fingerprints, leading to difficulty in biometric authentication using such a portion.
That is to say, a large part of the epidermal tissue of the human body, including the palm portion such as the thenar region and so forth, the base portion of a finger, the skin of the back of the hand, and the like, has patterns different from the patterns of the deep-layer structure therebeneath, except for a special case such as the fingerprints which are fingertip impressions, wherein the epidermal tissue directly corresponds to the deep-layer structure, allowing external observation thereof. Furthermore, it is difficult to make external observation of the deep-layer structure therebeneath due to scattering of visible light from the 6-layer epithelial structure and absorption thereof by the melanin pigment in basal cells or the like. This leads to difficulty in development of a finger-ring-type authentication device wherein person authentication is performed using the pattern of the skin in contact with the inner face of the finger ring at the time of being fit by the user.
On the other hand, the deep-layer structure beneath the epidermal tissue is essentially unique to an individual, and exhibits sufficient stability over time, as with a well-known example of fingerprints or the like. Note that a tattoo wherein a pigment is injected into the deep-layer structure, and a stretch mark caused by pregnancy, also have the same stability due to the properties of the deep-layer structure beneath the epithelium tissue. Accordingly, it is expected that the pattern beneath the epithelium tissue, i.e., the deep-layer structure of the epithelium tissue is suitably used for biometric authentication. However, the aforementioned patterns cannot be directly observed, neither left on an object by contact with the object, and accordingly, development of the authentication device using the pattern of the deep-layer structure has not been made, although the pattern of the deep-layer structure has the same performance of biometric authentication as with fingerprints.
The present invention has been made in order to solve the aforementioned problems, and accordingly, it is an object thereof to provide a biometric pattern detecting method and biometric pattern detecting device for acquiring the roughness structure distribution of the deep-layer structure beneath the epithelium tissue (patterns beneath the epithelium tissue) or the blood-vessel pattern beneath the epithelium tissue, which cannot be directly observed. Furthermore, it is an object of the present invention to provide a biometric authentication method and a biometric authentication device which enables stable biometric authentication while preventing a risk of “spoofing”, e.g., forgery or the like.