Add a .conf file to /etc/lightdm/lightdm.conf.d folder
(for example: 10-greeter-login.conf)
add the following lines to the [SeatDefaults] section:
greeter-show-manual-login=true greeter-hide-users=true allow-guest=false
Category: lightDM
Changing LightDM Login Background
Edit the file /etc/lightdm/unity-greeter.conf
Replace the image path in keyword background= with the exact path of the new background image.
e.g.
#background=/usr/share/backgrounds/warty-final-ubuntu.png background=/home/panda/Pictures/green-bamboo.jpg
