This has been bothering me very much. i have memory that Ubuntu 12.04 had this configuration? am i wrong? finally, is it possible for the login screen to have different wallpaper from the desktop? is this possible in Ubuntu 15.04? i would appreciate a stable understandable response. thanks :) -ben
I'm going to go ahead and post what worked for me. I found multiple threads trying to tell me how to change this, but this method is the only one that worked for me on Ubuntu 15.04. Some of the steps might not be entirely necessary, these are just the steps I ended up taking.
Get the picture you want to put as the login screen background. Place it in /usr/share/backgrounds/ and make sure the owner is Root:Root and the permissions match the other pictures in the folder (-rw-r--r-- or 644).
Navigate to /usr/share/glib-2.0/schemas/ and open the file com.canonical.unity-greeter.gschema.xml in gedit.
Find the key name background and change the default to the path of your picture in "/usr/share/backgrounds/. For the key names draw-user-backgrounds and draw-grid, change the default value to false.
Save your changes, then run the command
sudo glib-compile-schemas /usr/share/glib-2.0/schemas/
Restart the computer and your new login background should be there. Well, it was for me at least.
Hope this helps someone. No need to install anything, open dconf-editor, deal with the LightDM user or anything terribly complicated.
Source: Changing the Wallpaper
