Asked by: Kate Woods, Hertfordshire
When your finger is first scanned, the print is turned into a much-simplified numerical description. When you present your finger again, it's the numbers that are compared. These numbers don't contain enough information to reconstruct the original print, but the reference print stored in the database probably does. If not a perfect copy of the original fingerprint, then at least one that would fool that particular fingerprint scanner.
Fingerprint recognition systems need to allow for the fact that the live finger being scanned may be presented at a different angle to the original. For this reason, the matching algorithm will normally rotate and adjust the live scan image as it searches for the best fit with each of the records in its database.
When it finds a match, the number of matching features on the scanned print, as well as the distances between them, will be scored and weighted to give an overall match value. If this crosses a predetermined threshold, the print will be recognised.
Get more fascinating Q&As from BBC Focus magazine by following @sciencefocusQA