Ubuntu – Why does LightDM only show a custom wallpaper on the login screen if I have selected one of the default wallpapers?

After you added you images to /usr/share/backgrounds you need to open the Change Desktop Background dialog by right clicking in your desktop and selecting it.

After the dialog is open you can click the + to add the backgrounds you just copied to /usr/share/backgrounds

Add all the images you have in /usr/share/backgrounds, after you have done that you can select one and it will become your background.

If you are using 12.04 that same image will become the dynamic background for the Unity Greeter. If it does not follow the Setting the dynamic switching off section of How do I change the wallpaper in LightDM? except instead of actually switching it off you use the command

gsettings reset com.canonical.unity-greeter draw-user-backgrounds

has described in the answer.

Note to summarise:

• Step 1: Add you custom wallpaper to `/usr/share/backgrounds

• Step 2: Is conditional if you want your custom wallpaper to appear in the dynamic unity greeter (log in) in 12.04. Right click on your custom image and select "Properties" then select the Permissions tab. Navigate to the "Other" permission and change it from None to "Read-only". Note: If you don't do this Unity's default wallpaper will appear in Unity Greeter.

• Step 3: Now you need to open the Change Desktop Background dialog by right clicking on your desktop and selecting it.

• Step 4: After the dialog is open you can click the + to add the backgrounds you just copied to`/usr/share/backgrounds.

• Step 5: Select your image to and change your desktop background`

• Step 6: Log out and see the Unity Greeters background is your custom image

.

Change the wallpaper to match your "dynamic" backgoroud or, change it to - something like a black, or dark purple background so you don't notice the switch, How do I change the wallpaper of the login screen? , otherwise you will notice when it changes from the default to your dynamic.

Maybe its a bug, who knows? If you turn off the dynamic wallpaper it will still show a transition from a purple background to a custom wallpaper.

Note to benefit others: Answer accepted as it improved LightDM transition, however it did not fully resolve the issue. Complete resolution would be nice, its a "paper over the cracks" solution (the black background).