This is an easy way to change your wallpaper when you have wallpaper_daemon.py installed.
With wallpaper_daemon.py installed and you want to change your wallpaper it will mean that your login screen will be changed also. To change your wallpaper and keep your login screen you can change your desktop opacity when not rotating. This will make your dektop transparent so you will see the image (and much more) you have set as your Skydome background. To do this the CompizConfig Settings Manager needs to be installed, how to install.
To change the desktop opacity open your CompizConfig Settings Manager (System-> Preferences->CompizConfig Settings Manager) then click on the Desktop Cube button and select the Transparent Cube tab. Now change the Opacity When Not Rotating to 0.0000 and your done. You can also play around a bit to change the opacity to your likings.