Severed fingers and casts made from fingerprints need not apply:
[The iPhone 5S fingerprint sensor] can detect the ridge and valley pattern of your fingerprint not from the layer of dead skin on the outside of your finger (which a fake finger can easily replicate), but from the living layer of skin under the surface of your finger, using an RF signal. That only works on a live finger; not one that’s been severed from your body.
— http://www.citeworld.com/security/22399/iphone-fingerprint-scanner-better-biometrics
