Ever since I updated to iOS7 I've been taken by the effect of the new Parallax wallpapers! I think it's a great feature, but the default images left something to be desired. I have since upgraded my 4s to a 5s, and with the added processing power on tap, I went in search of more creative wallpapers. I found these sites with a raft of them - including a few Audi images.
If you don't know how to install them or transfer them to your iPhone\iPad\iPod, let me know and I'll gleefully mock you, before posting instructions.
The Next Web
The amount of data in images mean the sites take time to load properly, so be patient.