Copy the image you want to use into the /usr/share/gnome-shell/theme/
folder. For example: /usr/share/gnome-shell/theme/my_image_name.png
Then:
sudo gedit /usr/share/gnome-shell/theme/ubuntu.css
OR in some cases:
sudo gedit /usr/share/gnome-shell/theme/gnome-shell.css
Search for the following section:
#lockDialogGroup {
background: #2e3436 url(resource:///org/gnome/shell/theme/noise-texture.png);
background-repeat: no-repeat;
Change
background: #2e3436 url(resource:///org/gnome/shell/theme/noise-texture.png);
to
background: #2e3436 url(my_image_name.png);
(without path in case you copy your image to /usr/share/gnome-shell/theme/
like /usr/share/gnome-shell/theme/my_image_name.png
).
Alternatively, you can also simply set just a color (without wallpaper or texture) with:
background: #2e3436;
Set background-repeat
to repeat
or no-repeat
. In case your image is a texture, set it to repeat
. In case wallpaper: no-repeat
Reboot.