So here is a complete anecdotal suspicion:
I have had the iPhone since the first day of release. I have gone through 16 physical devices over that period (due to me breaking them a lot and going through several employers where I had never purchased my own phone since (well before) it was released). I am currently, for the first time in a long time, on my own personal device; an iPhone 4.
I upgraded it to iOS7 when it was available. The device is a slow POS and I want to stab my eyes out when I use it....
However; there is a behavior that I have only personally noticed recently: (Please tell me if you see the same thing)
Whenever I transition between literally ANY screen, I see a quick BLINK of the screen - in the same anim that you would see when you take a screenshot.
So I am wondering "Is my phone taking a screen cap of EVERY switch/transition I make? WHY"
Now, I know that iOS does do screen caps of things so that when you are switching in various ways that it already has a cache of the last state of that screen in order to thumbnail the previous view... BUT I understood this to be limited to certain circumstances. Currently I am noticing it on pretty much ANY transition.
Even if this is the actual, "Normal", my suspicion is that this fact can be used to entirely rebuild an entire session of activity for a user through their entire interactions. Even if you just grab these screens which are used at a system level - a great deal could be inferred from just these workflow screen caps.