jaaniic'ša pierakstu klade

-log out
-at the log in screen press CTRL+Alt+F1,
-enter user name and password
-Code:
export DISPLAY=:0.0
-press enter
Code:
-sudo -u gdm gnome-control-center
-press enter, expect errors,
-when terminal output stops press CTRL+Alt+F8

The Gnome Control Center should appear (it looks exactly the same as Appearance preferences from the Gnome Desktop, but , it relates to the login screen in this case.)
In Appearance
-choose Add and pick a new background, (or browse to one if it's in a different folder)
-close Gnome Control Center,
-press CTRL+Alt+F1
-at the terminal cursor type code:
sudo reboot