Bobby Neel Adams is a photographer who mainly works of portraiture and has done a series called Age Maps. Two photographs are taken of the same person at different periods of their life and then put together again in a very interesting way. The parts fit together surprisingly well into a very subtle change down the middle.
These images are really cool in that they capture two distinct time periods... I wonder if it could be developed so that the portrait is split into regions of 4, maybe 6 and even 8 to create an even more gradual aging picture.
It is a very clever idea!