Method and device for detecting fake skin prints
The method aims at identifying a fake element (F 1 ) reproducing a fake skin print positioned on the detection surface ( 13 ) of an optical device for detecting skin prints such as fingerprints. The method provides for sending ( 14 ) towards the abovementioned detection surface ( 13 ) an illumination beam ( 14 ) to be back-scattered and propagate through the fake element (F 1 ) bearing the fake print. The beam in question is a shielded beam including an illuminated region ( 22 ) and a shielded region ( 23 ). A sensor ( 16 ) captures the shielded illumination beam after the back-scattering, generating a signal indicating the dimension (x 0 , x 0 ′) of the transition region ( 24 ) between the illuminated region ( 22 ) and the shielded region ( 23 ) present in the shielded beam after the back-scattering. The possible presence of a fake element (F 1 ) reproducing a fake skin print is identified when the abovementioned transition region ( 24 ) has a dimension larger than a given reference value (x 0 ).
1. A method of identifying a fake element reproducing a fake skin print positioned on a detection surface of an optical device for detecting skin prints, the method comprising:
sending towards said detection surface an illumination beam to be back-scattered and propagate through said fake element, said illumination beam being a shielded beam including an illuminated region and a shielded region,
capturing a shielded illumination beam after the back-scattering, wherein, after back-scattering, said shielded illumination beam includes an illuminated region and a shielded region separated by a transition region,
generating signal indicating a dimension (x 0 , x 0 ′) of said transition region, and
identifying a possible presence of said fake element reproducing said fake skin print when said transition region has a dimension larger than a given reference value (x 0 ).
2. Method according to claim 1 including the operation of identifying the possible presence of said fake element reproducing said fake skin print when said transition region has a dimension larger than a given reference value (x 0 ) increased by a tolerance threshold.
3. Method according to claim 1 , wherein said given reference value (x 0 ) is determined as a value of the dimension of said transition region detectable by positioning an authentic skin print at direct contact with said detection surface.
4. Method according to claim 3 , wherein said given reference value (x 0 ) is determined as a mean value of said transition region detectable by positioning a plurality of authentic skin prints in succession at direct contact with said detection surface.
5. Method according to claim 3 , wherein said given reference value (x 0 ) is determined once and then stored in a plurality of revealing devices.
6. Method according to claim 1 , including an operation of emitting a signal to indicate an attempt to deceive upon identification of the possible presence of said fake element.
7. Method according to claim 1 , including the operation of generating said shielded illumination beam by interposing an absorbent shield on a propagation path of said illumination beam towards said detection surface.
8. Method according to claim 1 , wherein said illumination beam has a wavelength included between 380 and 750 nanometers.
9. Method according to claim 1 , wherein said illumination beam has a wavelength included between 400 and 420 nanometers.
10. Device for identifying a fake element reproducing a fake skin print positioned on a detection surface of an optical device for detecting skin prints, the device including:
a light source for sending towards said detection surface an illumination beam to be back-scattered and propagate through said fake element said light source being coupled to a shield to make said illumination beam a shielded beam including an illuminated region and a shielded region,
a sensor for capturing a shielded illumination beam after the back-scattering, wherein, after back-scattering said shielded illumination beam includes an illuminated region and a shielded region separated by a transition region, said sensor being susceptible to generate a signal indicating a dimension (x 0 , x 0 ′) of said transition region, and
a processing circuit sensitive to said signal indicating the dimension (x 0 , x 0 ′) of said transition region and configured to identify a possible presence of said fake element reproducing said fake skin print when said transition region has a dimension larger than a given reference value (x 0 ).
11. Device according to claim 10 , wherein said processing circuit is configured to identify the possible presence of a said fake element reproducing a fake skin print when said transition region has a dimension larger than a given reference value (x 0 ) increased by a tolerance threshold.
12. Device according to claim 10 , wherein said processing circuit is configured to store said given reference value (x 0 ) identified as a value of the dimension of said transition region detectable by positioning an authentic skin print at direct contact with said detection surface.
13. Device according to claim 12 , wherein said processing circuit is configured to store said given reference value (x 0 ) received as programming data.
14. Device according to claim 10 , including a prism having a face defining said detection surface and another face bearing said shield to make said illumination beam a shielded beam.
15. Device according to claim 14 , wherein said other face is a lateral face or an end face of said prism.
16. Device according to claim 9 , wherein said light source has a wavelength included between 380 and 750 nanometers.
17. Device according to claim 10 , wherein said light source has a wavelength included between 400 and 420 nanometers.