In this tutorial, we will show you how to easily change your default background image of your login screen with another custom image of your choice under Ubuntu 11.10 (Oneiric Ocelot). This tutorial is applicable only if you have the LightDM display manager installed on Ubuntu 11.10, otherwise there will be no effect.
1. Open the terminal and edit the unity-greeter.conf file using this command:
gksu gedit /etc/lightdm/unity-greeter.conf
2. Provide now the new path to your image in the following line:
Or simply move your image file to the "backgrounds" folder using this command:
sudo mv image.png /usr/share/backgrounds/
Then rename "warty-final-ubuntu.png" with your own image file name.
3. Save now your file and close it.
4. You login screen will now have a new look, here is mine: