How do optical scanners of fingerprint readers work?
The use of optical fingerprint scanners is the oldest method of capturing and comparing fingerprints. As the name suggests, it is a technique that relies on capturing an optical image, a photograph. This method then uses algorithms to detect unique patterns once a finger is placed on the surface, such as ridges or marks, by analyzing the lightest and darkest areas of the photo.
These sensors have a finite resolution like the phones we use every day. Note that the higher the resolution of the sensor, the more it can discern the details of your finger, thus increasing the level of security. On the other hand, these sensors capture images with much higher contrast than a normal camera.
Optical scanners typically have a very high number of diodes per inch to capture these details up close. Of course, the surface of the scanner is very dark when your finger is placed on it. To overcome this problem, scanners therefore integrate LED matrices like a flash to illuminate the image at the time of scanning.