There are a number of different ways to get an image of somebody's finger. The most common methods today are optical scanning.
Optical Scanning Reader
The heart of an optical scanner is a charge coupled device (CCD), the same light sensor system used in cameras. A CCD is basically an array of light-sensitive diodes which generate an electrical signal in response to light. The scanning process starts when you place your finger on a glass plate, and a CCD camera takes a picture. The scanner has its own light source to illuminate the ridges of the finger. The CCD system actually generates an image of the finger and compares it with the pattern stored in its memory. If it matches, the persona is authorized and the door is released.
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