Thanks to @buzzinh we found a way to change your login background.
Follow the instructions and/or watch the video
Download the wallpaper_daemon.py and extract it to your Documents folder, open a Terminal window (Applications->Accessories->Terminal) and copy+paste the following lines:
chmod +x wallpaper_daemon.py
When installed close the Terminal window and add wallpaper_daemon.py to your startup programs. Open your Startup Applications Preferences (System->Preferences->Startup Applications) and click on the Add buton. In the Name field fill in a name for the command. In the Command field click on the Browse button and browse to your Documents folder and double click on the walppaper_daemon.py file. At the Comment field you can add an comment to the command but you can also leave it empty. When done click the Add and then the Close button and reboot.
After the reboot…
Open your Desktop Preferences (System->Preferences->Appearanceor right click your desktop) and select the Background tab. Select the picture/image you want to use, to get a preview of your new login screen open a Terminal window (Applications->Accessories->Terminal) and type:
To exit the preview hit the Escape key.
Have fun playing!!