Gnome, KDE and XFCE users will have no problem changing the wallpaper on their desktop. However, if you are using a lightweight desktop manager such Openbox or Fluxbox, you will find that there is no way that you can set the wallpaper for your desktop. In this case, Nitrogen will come in handy.
Nitrogen is a simple, lightweight application that allows you to change the background of your desktop. Some of its key features include support for Multihead and Xinerama, a recall mode that can remember the last wallpaper set and command line mode for script use.
If you are using Ubuntu 8.10 (with Openbox) or any other debian-based system, here is how you install and configure Nitrogen.
In your terminal,
sudo nano /etc/apt/sources.list
add this two lines to the end of the file.
deb http://ppa.launchpad.net/k-belding/ubuntu intrepid main
deb-src http://ppa.launchpad.net/k-belding/ubuntu intrepid main
Press Ctrl + O to save the file and Ctrl + X to close the file.
sudo apt-get update
sudo apt-get install nitrogen
This should install Nitrogen on your system
Setting background wallpaper
Assume that your wallpaper folder is at /home/username/wallpaper.
In the terminal, type
A window will pop up showing all the wallpaper in the folder. Pick the one that you want to set as background image and click Apply.
To get it to autostart everytime you log in, in your terminal,
Paste this into the end of the file
nitrogen --restore &
If the autostart.sh file does not exist, you will have to manually create one before you can carry out the above step.