I'm not totally sold on the idea of biometric identification, our fingerprints and eye scans can be used against our wishes, in extreme and exceptional (I hope!) cases people have had their fingers removed. I have a scar on one of my fingertips, that finger can bring up an error message when a scanner decides that it is not an expected fingerprint type. If someone has an injury which leaves a scar on their most commonly used finger they could be in trouble with biometric scanning.