Something interesting when setting up Touch ID...

I have seen what you're talking about. I'm not sure if the picture on the screen really means too much. I think it's just a nice little thing for you to look at, but the lines might not be fully representative of what part of your finger the scanner has looked at. I think the lines are more of a progress bar to give you an idea of how much longer it's going to take.

 

I am pretty sure the image you see of the print means absolutely nothing.

 

Yes, it happens to me almost always when I try to register a finger. As previous poster said, it is just a meaningless progress bar.