iPhone -- possible to tell the difference between a fingertip and a whole fingerpad?

Is it possible to detect exactly how much finger is 开发者_JAVA技巧in contact with the screen? Say I wanted to make a fingerprinting app, how would I detect the outline of a person's fingeR?

No, the UITouch system does a lot of processing to determine a single point location for each touch given the larger touched area. This is meant to aid the user as there can be some difference between where one thinks he is touching and where the screen is actually touched.