Sir

In your News & Views Q&A 'Biometric recognition' (Nature 449, 38–40; 2007), Anil K. Jain asserts that biometric technologies are more difficult to abuse than traditional methods of identification. However, we all leave a biometric trail in our daily lives: our fingerprints on a drinking glass, our voice on a telephone answering machine, our iris patterns on a photograph. We have little ability to change such characteristics and little control over this trail, which makes biometrics useful to forensic science.

But it's exactly these properties that make biometrics a poor replacement for passwords and ID cards, since it's easy for an intruder to collect someone's fingerprint or iris scan without their knowledge, and then inject it into a biometric identification system. Even if the victim becomes aware of the problem, it's impossible to revoke the biometric. If your credit card is stolen, the card company can send you a new one with a different number, but you can't get a new set of fingerprints.

It is precisely because biometric information is irrevocable and unwittingly provided in our daily lives that it is so useful to organizations that regulate the individual (for example, the US Immigration Service), but of little use where the individual controls identification and authorization.