Biometric authentication I see in some “Authentication schemes with biometric” papers that those authors wrote a phase as password and biometric update phase.
My question is that why we may needs biometric update phase?
Is not biometric (say finger print or iris or face and …) permanent properties?
Some devices I've been working with do indeed update biometric information.

The reasons is that there may be additional information:


acceptable fingerprint was scanned (required features are found), but the scan shows some area of finger not involved in previous scans.
some other additional information helping make more exact scans in the future