To set preferences for the desktop background, you modify the values of the preference keys in the /desktop/gnome/background location. For example, to set a mandatory image for the background, run the following command:
# gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory --type string --set /desktop/gnome/background/picture_filename filename.png
To set a default value for this preference, run the following command:
# gconftool-2 --direct --config-source xml:readwrite:/etc/gconf/gconf.xml.defaults --type string --set /desktop/gnome/background/picture_filename filename.png
You can also set other background preferences. For information on the other background preferences, see the desktop_gnome_background.schemas schema definition file.