Save the file as TGA, the dimensions need to be powers of two, then add the file's path to kgPanels. Dunno how that adding process works exactly, but I'm sure someone else will be able to clear that up.
There's an "Art Library" section in kgPanels - go to it, it should have a place for "New Art", just input the path to the artwork in that box and click "Okay".
It's been a long time since I've used that method, myself, as I use SharedMedia to inject artwork into the game.