This image is processed to extract user-specific information or minutiae. New imaging methods allow capture of fingerprints with optical, opto-electronic, electric, or thermal transducers. For example, variation in the capacitance between the user's fingers and sensors on the surface of a special mouse can help draw the contour of the fingerprint. Another technique relies on a low-tension alternating current injected into the finger pulps to measure the changes in the electric field between a resin plate and the derma. These variations reproduce the details of the fingerprint.
Thermal techniques rely on a transducer to measure the temperature gradient on the mouse's surface.
Finally, opto-electronic methods employ a layer of polymers to record the image of the fingerprint, which a transducer converts into a proportional electric current. Recognition of hand geometry is already in use for access control in large-scale commercial applications. The user positions a hand on a plate between a set of guiding pins. This plate is surrounded by mirrors on three sides to capture the hand from the side and top with a digital camera. The hand geometry is described using 90 characteristics in the form of a 9-octet vector.