Suppose, he says, all your data is encoded to your thumbprint, and someone hacks into the database. True, you can stop them from using it by cancelling it. But what next? "The bank can issue you a new card with a new number. But (with biometrics) this is your thumb -- you can't get a new one." Identity theft is bad enough with replaceable passports, bank cards and drivers' licences. With a biometric ID card, the only way to get rid of the stolen identity would be permanently to delete the legitimate one as well. That's a nightmare for governments and citizens.
Recently, nearly 1,000 traditional Pearson International Airport passes were misplaced. Security supervisors quickly cancelled them (and eventually recovered them). If they'd been biometric, and stolen rather than misplaced, cancelling them wouldn't have been enough. You'd have had to change employees -- hire ones with different thumbs or eyeballs (or go the Tom Cruise route).
The fingerprint or iris merely provide the nesessary values for the mathematical algorithm. If a card is lost, new values can be taken from the eye or finger and the database administrator can invalidate the previous algorithm. In other words, an eye or thumb transplant is not required.
http://canadagazette.gc.ca/partI/200.../regle3-e.html
It uses smart card technology, which integrates a small computer chip, including a microprocessor and memory to store two kinds of biometric data: fingerprint and iris templates. These templates are generated by algorithms that encode distinctive features from an individual's iris and fingerprint images. The templates cannot be used to recreate images of the iris or fingerprints.