To fight against computer crimes, a computer system needs a sure way of identifying its right users and rejecting those who are not entitled to use it. The identification system should be quick, simple, and convenient. At present, signatures are widely used to identify credit card holders, but it takes an expert to detect a good forgery. Sometimes even a human expert is fooled, and there is no reason to believe that a computer could do any better. Photographs are also sometimes used for identification. But, people find it inconvenient to stop by a credit-card company and to be photographed. Companies might lose business if they made the pictures under absolute requirement. Also, photographs are less useful these days, when people frequently change their appearance by changing the way they wear their hair. Finally, computer programs for analyzing photographs are still highly experimental. Cash-drawing systems often use two identification numbers: One is recorded on a magnetic stripe on the identification cards, and the other is given to the CRS holder. When the user inserts his card into the cash-drawing terminal, he keys in the identification number he has been given. The computer checks to see that the number recorded on the card and the other keyed in by the user refer to the same person. For a long time, fingerprints have provided a method of positive identification. But they suffer from two problems. One is that there is no simple system for comparing fingerprints electronically, the other is that because most people associate being fingerprinted with being arrested they almost surely would resist being fingerprinted for routine identification. Voiceprints have been suggested. With these, the user has only to speak a few words for the computer to analyze his voice. There are no psychological problems here. And technically it's easier to take and analyze voiceprints than fingerprints. However, it has yet to be proved that the computer cannot be fooled by imitation. Also, the voice is subjected to the noise and distortion of a telephone line. Even lipprints have been suggested. But it's doubtful that kissing computers will ever catch on. Which of the following is NOT mentioned as one of the identification system requirements?