[TrainedMonkey]

Doing that is way harder then guessing 4 digit pass code. Besides depending on technology used in Apple's device you might need to get way more sophisticated. With processing power of mobile devices nowadays, how much would you need to invest to make a fake that is not easily statistically distinguishable from real thing? What is stopping that scanner from taking 20-100 pictures and then analyzing them in background? I really do not think run of the mill fingerprint faking will be sufficient to overcome modern fingerprinting with sufficient security emphasis put into them.

[robryk]

I'd guess false negatives. You _really_ don't want persistent false negatives. I wonder what's the solution to the `I cut my index finger' problem. Does it require multiple fingers to be enrolled?