It is possible to have a different desktop background on each workspaces using a compositing manager called Compiz Fusion. However, to describe this software as a background manager is to do it a great disservice!
"Compiz is an OpenGL compositing manager that use GLX_EXT_texture_from_pixmap for binding redirected top-level windows to texture objects. It has a flexible plug-in system and it is designed to run well on most graphics hardware."This is no idle boast: Compiz is not only running on my DELL Inspiron 1501, but it is also delivering the graphical enhancements promised on the Compiz Home Page.
"In a nutshell, Compiz is a compositing manager, which means that it enhances the overall user interaction by adding fancy effects to your windows, from drop shadows to awesome desktop effects like the Desktop Cube or the Expo view.""Awesome" is not overstating the case!
The screen-cap (above) is lifted directly from my laptop. The cube can be rotated in any direction using a USB mouse and any workspace selected. It is no exaggeration to say that that this laptop could barely load Windows Vista a month or so ago, but it is now running graphics that would put most Windows desktops to shame.
The configurations possible from the CompizConfig Settings Manager are bewildering and it has taken me several hours to get to grips with just the basic settings. However, the result is a multi-workspace environment, each with its own background and all accessible using either mouse or keyboard.
To install Compiz on Ubuntu, open a terminal and type:
sudo apt-get install compiz compizconfig-settings-manager compiz-fusion-plugins-extra compiz-fusion-plugins-main compiz-plugins
You may also want the Simple CompizConfig Settings Manager!
sudo apt-get install simple-ccsm
Then, makes sure that the Enhanced features are enabled in the Appearance dialog (System > Preferences > Appearance > Visual Effects). Once done, you'll find the Config Settings Manager under the System > Preferences menu.
Whilst the interface is not particularly intuitive, it is worth persevering. Setting wallpaper and animating the cube will test your patience, but there is help on the Compiz Wiki pages.
Sources & References:
Compiz Fusion Ubuntu Documentation