Where is the background image saved? Here's my situation:

I had an image from a website which I set as my background inside the browser. I am wondering now where I can find the image in the file system, because I can't find it online anymore. I am rooted.
I was annoyed by the exact same problem, so I have programmed an app that automatically saves your wallpapers and your live wallpapers too. It makes it easy to revert to a previous wallpaper. It is called Wallpaper Saver, by Appdictive, and it's free in the Play Store. (It does not require root access.)