Sensing system for ascertaining currency content of ATM

A method of operating an ATM, comprising:

• a) maintaining a controller in the ATM which controls operation of components of the ATM;
• b) maintaining at least one cassette in the ATM, which contains currency which the ATM dispenses to customers, said cassette containing a door through which currency is withdrawn when being dispensed to a customer;
• c) maintaining a target within the cassette, which changes position as the currency in the cassette is depleted;
• and
• d) maintaining a sensor outside the cassette which takes a digital image of the target through said door, and provides the digital image to said controller.

For an Automated Teller Machine, ATM, which contains a controller which controls operation of components of the ATM, an apparatus comprising:

• a) at least one currency-storage cassette containing a door through which the ATM withdraws currency;
• and
• b) an optical target within the cassette, which
• i) is visible externally through the door, and cooperates with a camera external to the cassette to provide a target-image to the camera,
• ii) changes position as currency is depleted from the cassette, and
• iii) enables the controller to compute the amount of currency in the cassette, based on features of said image, which the controller uses to infer said position.