Change the background of the login screen

The proper way of changing default unity-greeter background is through overriding glib-2.0 schema, as specified in the Lightdm Ubuntu Wiki

The steps are as follows:

1. Create /usr/share/glib-2.0/schemas/10_unity_greeter_background.gschema.override file with the following contents:

   [com.canonical.unity-greeter]
   draw-user-backgrounds=false
   background='/foo/wallpaper.png'
   

2. Run sudo glib-compile-schemas /usr/share/glib-2.0/schemas

3. Reboot or login to TTY2 (accessed by pressing Ctrl+Alt+F2 ) and run sudo service lightdm restart

This has been tested on my Ubuntu 14.04

Update: November 17 2015

I have put together a script that simplifies the process of changing the greeter background. It has been tested in its final form on two versions of Ubuntu, 14.04 LTS (actual physical machine ) and 15.10 (Virtual Machine ) It can be found in my GitHub

It seems like all the gsettings have no effect in Ubuntu 15.10, (maybe because I installed Ubuntu Studio with xfce4 first).

I solved it by adding this line to /etc/lightdm/lightdm-gtk-greeter.conf:

background=/usr/share/backgrounds/Tranquil_by_Pat_David.jpg

or in one sudo command:

sudo su -c 'echo "background=/usr/share/backgrounds/Tranquil_by_Pat_David.jpg">>/etc/lightdm/lightdm-gtk-greeter.conf'