An interesting project by Design Language:

"Because the primary input method of the iPad is a single piece of multitouch glass, developers have incredible flexibility to design unique user interfaces. It’s hard to appreciate the variety of UIs though, since turning the screen off removes virtually all evidence of them. To spotlight these differences, I looked at the only fragments that remain from using an app: fingerprints."

Why do I blog this? It's interesting to observe how this quick hack enables to observe touch interface usage patterns very easily. The idea here is to benefit from physical traces to describe the accumulation of interaction over time. It would be fun to add a temporal dimension to this.