There are two js functions.
The first has a timer that calls the other function every 12 seconds
The second gets the background image's top,left and uses it in a randomiser.
Then moves the image accordingly. It also tries to take in account not to let the random number pull the image borders into the main view ( may need some work)
The math probably needs adjusting for yours but hopefully this gives you an idea..
randomMove.hype.zip (171.3 KB)