gconftool-2 --direct \\ --config-source xml:readwrite:/etc/gconf/gconf.xml.defaults \\ --type string \\ --set /desktop/gnome/background/picture_filename
gconftool-2 --direct \\ --config-source xml:readwrite:/etc/gconf/gconf.xml.defaults \\ --type string \\ --set /desktop/gnome/background/picture_filename