Wallpaper / Background ?

I am trying to determine where the file is that Windows
uses to get its background jpegs, HTML doc., for use as a
Wallpaper.

Selecting from the desktop, rt click: Active
Desktop|Customize my Desktop|Background Tab, a list is
given of available wallpapers.

I thought the list might be "My Pictures" in "My
Documents." I moved a jpg into that folder and it showed
up as a new file in the available wallpaper backgrounds.

I pulled it out and it disappeared from the backgrounds.

Next, I removed from the My Doc. folder the entire "My
picture" file, renamed it and moved it to another disk.

Still, its contents are coming up as the wallpaper
backgrounds.

I gave one of the pictures in the renamed folder a
different name: it showed up in the Background Wallpapers
with the old name and the picture would come up.

I changed the extension of that jpeg and it stilled showed
up in the Background|Wallpaper selections, with the same
name, but now the picture was broken. -progress--

So my question is, where is the folder/files that Active
desktop uses for background wallpapers and how do I edit
it?
Is it a registry list somewhere? Any kb on this?

Thanks,
Bob