Changing background in Gnome3 can be done in various ways the most common ones being the GUI ways. If you however want to change your Gnome3 background without any graphical user interface you can  execute the following command inside the terminal client:  gsettings set org.gnome.desktop.background picture-uri “file:////etc/skel/drift.png

In the above example the /etc/skel/drift.png is the location of my background so tweak it according to your needs. If you are not using Gnome3 but you are using a windowmanager such as Fluxbox with gnome-settings-daemon then you can add the following line to your startup file:

(sleep 5 && gsettings set org.gnome.desktop.background picture-uri “file:////etc/skel/drift.png”) &

The above line tells your not-Gnome3 windowmanager to wait for 5 seconds and then get the background picture from the given file and apply it while using gnome-settings-daemon. The result of this approach is that your background will not get overwriten by Gnome3 settings but you can use your own custom background easily instead. You might need to tweak the examples given here according to your Linux configuration.