Use User Wallpaper as Background in App iOS 7

I was using the Harmony Link app for iPhone with iOS 7, and a very cool visual effect occurred, my background showed up as the background to the window and it even had parallax motion. I noticed a similar occurrence in the Newsstand app.

Does anyone have any ideas on how to import the user's background into an iOS app? (Possibly even with parallax motion?)

I have seen other posts which do not address this question directly.

You can make your application's window transparent as described in this post: iOS 7 transparency but be careful as this is a non-public API.