Ok, I installed MAMEWAH and unzipped the LAYOUTS.ZIP file.
Everything works great.
I see a MrSalty layout I want to use, so I unzip it into its own layout directory.
The layout works (all the text and box positions are fine), but the background image does not show up (I just see a grey background).
I have used the MAMEWAH layout designer, and modified the CFG file and changed the llayout name from within the MAMEWAH options menus. All three of these cause the layout to work, with no background image showing.
As an aside, no layout I have tried has a functioning background image.
What am I doing wrong?