One way you could do it, is make the content div extend to the top of the tabs and give it a top padding to make sure the content starts below the tabs.
Then make the active tab transparent, and give the other tabs a background color, as well as adding a white div in between the tabs to hide the rest of the background.
I would first probably attempt to just position the same image in each tab. By using background position you should be able to position it pixel perfect.
I didn’t think of that, that’s probably a much better solution.
You’d probably not want to show the background image to a user without javascript though as it will look really weird if they aren’t positioned. (This is supposing you will position the background image with javascript, which makes the most sense)