And this is the reason why fingerprints should not be used as a password. If the password that you are using (string, pin, fingerprint, iris) can not be change

And this is the reason why fingerprints should not be used as a password. If the password that you are using (string, pin, fingerprint, iris) can not be change then this could be use as username not password. It is very convenient to use things like fingerprints to lock your devices but if your credentials will get compromised once then you can not ever secure it again. Plus we leave finger prints everywhere all the time, it's just a matter of time when databases with fingerprints matching fb profiles will show up on the internet. Think about it as rainbow tables for unlocking stolen devices.