You can do this via Group Policy and apply it to the systems you want to have the background. You will want to pull up the Group Policy Management console by running gpmc.msc from a run prompt. Find the GPO that you want this setting applied in, or create a new one. Edit the policy by right clicking it and choosing Edit, then browse to User Configuration > Administrative Templates > Desktop > Desktop.
In there you are going to want to select "Desktop Wallpaper", Enable the setting and then put the path to the image you want to use and select how you want it to appear.
Next you will need to Enable the "Enable Active Desktop" setting and thats it.
