You can change the default desktop background to one that you want to use. For example, you may want to use a background with your company or university logo instead of the default GNOME background.
Create the key file
# Specify the dconf path
[org/gnome/desktop/background]
# Specify the path to the desktop background image file
picture-uri='file:///usr/local/share/backgrounds/wallpaper.jpg'
# Specify one of the rendering options for the background image:
picture-options='scaled'
# Specify the left or top color when drawing gradients, or the solid color
primary-color='000000'
# Specify the right or bottom color when drawing gradients
secondary-color='FFFFFF'
Provide information about the different picture-options values. Possibly also about when and how colors are used and what the gradient does.
To prevent the user from overriding these settings, create the file
# Lock desktop background settings
/org/gnome/desktop/background/picture-uri
/org/gnome/desktop/background/picture-options
/org/gnome/desktop/background/primary-color
/org/gnome/desktop/background/secondary-color