Basic banknote counters provide a total count of the notes in the supply hopper. More advanced counters can identify different bill denominations to provide a total currency value of mixed banknotes, including those that are upside down. Some banknote counters can also detect counterfeit bills either magnetically and/or using blacklight. Blacklight (UV) based detectors exploit the fact that in many countries, real banknotes have fluorescent symbols on them that only show under a black light. Also, the paper used for printing money does not contain any of the brightening agents which make commercially available papers fluoresce under black light. Both features make counterfeit notes both easier to detect and more difficult to successfully produce.
A stack of bills are placed in a compartment of the machine, and then one bill at a time is mechanically pulled through the machine. By counting the number of times a beam of light is interrupted, the machine can count the bills. By comparing an image of each bill to pattern recognition criteria, the machine can figure out the denominations of the bills and how much genuine money was placed in the compartment.
Read more about this topic: Coin Sorter