Hi, could anyone give me the general idea on how to implement this feature?

Basically, i want the desktop background to change whenever user place the mouse on program's shortcut.
It's not clicking, just Focusing.
You know, just place your mouse cursor on the shortcut and the background will change.

I have a halo 4 game shortcut on my desktop
I place the mouse to that shortcut, and the background will change to halo 4 wallpaper
When i click it the game will run normally.

By default windows shows the location of the program's exe when the shortcut is focused.
I couldn't find the registry files that control this feature, nor the method to tweak windows shortcuts...

thanks before.