How to change Ubuntu Budgie login screen background?

I want to change the Ubuntu Budgie login screen background to the one I'm currently using on my account; Just like it was with the previous Ubuntu versions with Unity with the draw-user-backgrounds option.
I already tried searching for that option or anything with "background" on it with dconf-editor but found nothing.

I have simple Ubuntu 18.04.1

In my opinion the best way to do this:

step1: make backup of the file /usr/share/gnome-shell/theme/ubuntu.css - if you have another desktop for ubuntu you can find file ubuntu.css just using command locate ==> locate ubuntu.css

step2: vim /usr/share/gnome-shell/theme/ubuntu.css and find part below

   #lockDialogGroup {
   background: #2c001e url(resource:///org/gnome/shell/theme/noise-texture.png);
   background-repeat: repeat; }

step3: change it to

   #lockDialogGroup {
   background: #2c001e url(file:///usr/share/backgrounds/warty-final-ubuntu.png);
   background-repeat: no-repeat;
   background-size: cover;
   background-position: center;
    }

clarification: as you can see, we changed
"background: #2c001e url(resource://" part to the ==> "background: #2c001e url(file://"
and then set up path for the image.
I used /usr/share/backgrounds/ for the path with image. Also I added some css properties to center the image.

This is only the css file configuration. That's it)

Open the Login Window app in the menu under Administration.

If it is missing from the menu then install it:

sudo apt install lightdm-settings

Enter your credentials when prompted. Click on the default background image icon, then navigate to /. Click on home>username>Pictures. Select your desired pic, click Open the in upper right corner, close the app. Log off and you will see your desktop background on the Login screen.

Thanks.

I tried all of those and none worked. This does, for sure:

As root user, just copy your_image.png to /usr/share/backgrounds and ....

# cd /usr/share/backgrounds
# cp warty-final-ubuntu.png warty-final-ubuntu.png.stock
# rm warty-final-ubuntu.png
# ln -s your_image.png warty-final-ubuntu.png
# reboot

...where your_image.png is the name of the actual image you want to display. The warty one is big: 4096 x 2304. I matched mine to the same size.

had the same problem when upgrading to 18.04. 64bit. And the answer is, it depends. Start with 'cat /etc/X11/default-display-manager' and check which greeter manager you got.

Case1. If using gnome-greeter (gdm3, and for example with ubuntu-unity-desktop which is in my case) modify the ubuntu.css as mentioned before and make sure you have replaced 'resource' ident by 'file', otherwise it won't work no matter how hard you try (i promise). Restart your machine. (gnome-tweak-tool works for modifying the background etc.)

Case2. If using the lightdm greeter one can use 'sudo apt install lightdm-gtk-greeter-settings' an adapt changes as needed. Two alternatives are the dconf editor (search for 'greeter', what will show you all the config settings available, and the 'sudo apt install unity-tweak-tool'.

Change between your greeter managers and the different ways changing styles with 'sudo dpkg-reconfigure lightdm' or 'sudo dpkg-reconfigure gdm3'.

Hope it helps