Cfxtrjtrk

Cheap and dirty solution:
Got to Terminal, then:

sudo nautilus

Then use Nautilus to copy your preferred background to

/usr/share/backgrounds/

Then rename the image that is being used to backup-imagenameold.png
Then rename your preferred image to the filename of the original background.

I know it's not clean or lean, but it does the job asap ;)

Cheers, Rüssel

Hmmm .. I try install dconf-editor to change that background.
Open Terminal and type this script ..

sudo apt-get install dconf-editor

Run dconf-editor:

sudo dconf-editor

And show the Window ... Open com > canonical > unity-greeter
Then change:

draw-user-backgrounds: 'true'

background: 'path-to-image'

Its very simple.

1. Open a terminal


2. 
   

   become root and change current folder

   
   
   

   sudo su
   
   cd /usr/share/backgrounds/
   
   

   
   



3. Copy the picture file to this location




4. Change the file name to warty-final-ubuntu.png

That will change the login screen background image.

Source

I believe what you are looking for is:

sudo apt-get install lightdm-gtk-greeter

sudo vim /etc/lightdm/lightdm-gtk-greeter.conf

Change the line:

background=/usr/share/backgrounds/warty-final-ubuntu.png

to whatever you want. Hope this helps

Canonical added the support for it in Ubuntu 16.04. Take a look at this link -> https://help.ubuntu.com/16.04/ubuntu-help/user-changepicture.html

I accidentally have found the solution which works great. It even preserves animation of emerging wallpaper during login screen (which i wanted the most). Step by step what i did:

1. 
   

   (lightDM) Change the wallpaper login screen to default. Type in Terminal:

   
   
   

   sudo -i
   
   xhost +SI:localuser:lightdm
   
   su lightdm -s /bin/bash
   
   gsettings set com.canonical.unity-greeter draw-user-backgrounds 'true'
   
   gsettings set com.canonical.unity-greeter background ''
   
   exit
   
   

   
   
   

   This will change logon wallpaper to default. (We need it for animation thing)

   
   


2. 
   

   Make a startup program named for example 'WallpaperChange', which executes this line:

   
   
   

   gsettings set org.gnome.desktop.background picture-uri 
   
             file:///usr/share/backgrounds/ur_desktop_wallpaper_here.jpg
   
   

   
   
   

   During every startup it changes your desktop background on ur_desktop_wallpaper_here.jpg

   
   
   

   Note: Whole path to ur_desktop_wallpaper_here may be changed.

   
   



3. The most important thing. Change your desktop background via GUI in Preferences Options on the wallpaper, which you want to have on logon screen.




4. Restart your computer.




5. Uncheck startup program 'WallpaperChange'. You don't need it any more now. During the next change of the wallpaper you will use it again.

I had only tested it on ubuntu 13.04 and found a solution by accident. I cannot provide you a technical answer why it works. It may depend on what you had done with your computer before setting logon wallpaper. I will reinstall ubuntu, try this code again and learn if my solution needs any further editing. (Added 4th line in p.1)

Greets.

I am using Ubuntu 14.04 (all Desktop settings are standard and I am using the standard shell) and I think it is even simpler than all solutions stated above.

The only thing I do, is downloading a picture or getting one of my own photos, fitting with the screen size, click the right mouse button on the downloaded picture and select "Set as background".

This process seems to copy the image into the users Picture/Wallpaper folder and, given the right size of the image, will show this picture also at next login.

I got the simpler way in Ubuntu 14.04 to solve this problem. You just have to change the permissions of image by typing command in terminal as follows.

chmod 644 'path-of-file-to-change-permission'

Replace path-of-file-to-change-permission with the path of your picture.

For example your background images are in /home/Admin/Pictures then type command as follows.

chmod 644 /home/Admin/Pictures/*.jpg

This will work.

Simple way, you can change the login background using Nautilus:

• open Nautilus (in root mode)


• go to /usr/share/backgrounds
  


• cut/move/delete "warty-final-ubuntu.png"


• then choose the picture you want (.png format)


• rename it to "warty-final-ubuntu.png"


• then move it back to /usr/share/backgrounds
  

I was able to change the login screen by accident. It seems to work every time for me. I choose a pic I wanted to use, opened it in Shotwell then Saved it as a PNG format. Then selected that pic as my background. Then I logged out and back in and Bam. The Login screen is the pic I chose.No more ugly orange color. Now, I need to figure out how to remove the grid on the login screen.

step 1. Install ubuntu tweak
sudo apt-get install ubuntu-tweak

Step 2. Start Ubuntu tweak
from commandline: ubuntu-tweak

Step 3. Change the background image
Go to Tweaks > Login settings > click to change background image

1. sudo cp your_wallpaper.jpg /usr/share/backgrounds/


2. sudo chmod 644 /usr/share/backgrounds/your_wallpaper.jpg


3. sudo nano /usr/share/gnome-background-properties/trusty-wallpapers.xml


4. Go to the bottom of the file and above the last </wallpapers> tag, copy the text:
   
   

<wallpaper>

    <name>Name_of_your_wallpaper</name>

    <filename>/usr/share/backgrounds/your_wallpaper.jpg</filename>

    <options>zoom</options>

    <pcolor>#000000</pcolor>

    <scolor>#000000</scolor>

    <shade_type>solid</shade_type>   

</wallpaper>

</wallpapers> <-- This should be the last line - copy the above text

5. Save file and exit.


6. Open System Settings->Appearance->Look tag->Wallpapers from the expanding window. And finally choose your wallpaper which will appear now with the name Name_of_your_wallpaper.

In the past this would work for me. Im am not sure if this will work in a unity environment.

Run this.

sudo cp /usr/share/applications/gnome-appearance-properties.desktop /usr/share/gdm/autostart/LoginWindow

Log out, make your changes.

Log back in

Run this.

sudo unlink /usr/share/gdm/autostart/LoginWindow/gnome-appearance-properties.desktop