Patent ID: 7576843

Claim:
An optical device for biometric sensing by contact, the device comprising: an optical element having a face that constitutes at least in part a surface for apposition of a body part from which it is desired to sense a biometric characteristic; an electromagnetic radiation source associated with said optical element to illuminate said face through the optical element with electromagnetic radiation substantially perpendicular to said face; and sensor means suitable for picking up reflected radiation coming from said face of the optical element; wherein said face of the optical element is coated with a thin layer defining a predetermined repeating pattern and made of a material such that, in relation with the material constituting the optical element, said thin layer defining said predetermined pattern is transparent to the electromagnetic radiation emitted by the radiation source when a body part is placed on said face of the optical element and is significantly less transparent for an interfering external electromagnetic radiation that is inclined relative to said face of the optical element and without any body part being apposed on said surface of the optical element, whereby the image received by the sensor means can be discriminated as to whether it constitutes a real image or a latent image.