system
Given the following post, respond as if you're commenting on Reddit:
human
How do fingerprint readers work?
gpt
The simplest ones literally use a camera (usually infrared) to take a picture of your finger. Next, some basic image processing is used to convert the image into a normalized binary raster (i.e., thresholding is applied). Then, an algorithm selects identifying characteristics called "minutiae" from the raster. These minutiae are classified into a few categories (e.g., "ridge stop", "ridge fork"). The locations and types of the minutiae on the fingerprint essentially become a multi-dimensional vector, and similarity metrics can be applied between the collected vector and a database of known fingerprints. If a similar enough collection of minutiae is found, it is treated as a match.

Reference: Mark Stamp. "Information Security." 2nd ed., p. 244-245.