Exception processing is the method of authentication employed for users incapable of successful biometric authentication. Exception processes can be secondary biometric technologies, passwords, PINs, or live verifications. Some deployments can afford a high exception processing rate, whereas others would be rendered inoperable if a large percentage of users required alternative verification. In any case, it is absolutely certain that some percentage of users - perhaps 0.5%, perhaps 10% - will be incapable of using a system successfully.