This is a good brief post by Bruce Schneier to read when the subject of biometrics come up:

https://www.schneier.com/blog/archives/2009/01/biometrics.ht...

The thrust of his argument in this post is:

> The lesson is that biometrics work best if the system can verify that the biometric came from the person at the time of verification. The biometric identification system at the gates of the CIA headquarters works because there's a guard with a large gun making sure no one is trying to fool the system.

Which may be a good thing to keep in mind if you are using fingerprints to id someone using their phone's camera.