Maybe I wasn't clear in my description of the problem, sorry about that.
I know how to change the wallpaper, but the problem is that when I deselect "Manage the desktop and show icon files", the icons vanish (exactly what I want) but on reboot I get a grey background - no wallpaper
I have to re-enable "Manage the desktop and show icon files", then re-disable it to get a desktop without icons, but WITH wallpaper.
This series of screenshots shows what I mean.....
It's not an xcompmgr problem, it does it without anything loaded .
The first question that comes to my mind is this ... if you don't want any icons on your desktop in the first place, why do you have them in your Desktop folder?
PCManFM manages the desktop, which means it is responsible for displaying the icons on your desktop, along with managing your wallpaper.
The easiest way to get rid of the icons on your desktop, without upsetting the other desktop settings, is to simply delete the icons from your Desktop folder in your /home directory. Also, if you have applications showing up on your desktop, delete their .desktop files from the Desktop folder, if you don't want them showing up. If you don't want to totally eliminate them from your desktop, then create a folder in the /home/Desktop directory, and place them in there. That way, they are still accessible, but don't take up a lot of screen real estate.
The folders in your /home directory won't show up on the LXDE desktop, unless you place them in the /home/Desktop folder.
There is, however, one icon you cannot eliminate from your desktop ... and that's the "My Documents" folder. This is a known bug in PCManFM.
I hope this helps!