It was a showerthought, I actually know very little about hashing. It's a technique used in cryptography that instead of storing sensitive data (like everyone's passwords) you store the result of putting their password through some mathematical function that's really easy to do one way, but really hard to do in reverse. For example, it's easy to find the cube of a number, but relatively hard to find the cube root of the result. Maybe you could do something like that with fingerprints. Like make an app that combines their fingerprint with a timestamp in a way that you can verify matches all their other fingerprint-timestamp hashes. That way you can at least say "yes, this is the same physical person I was talking to ten days ago." It doesn't guarantee they're not a fed or anything, but then again neither will a drivers' licence.