DuMBSwitcher

DuMBSwitcher (Dual Monitor Background Switcher) is a tool I built to allow slideshow capabilities for background images in Ubuntu, when you have two monitors. It is implemented as a Python script that automatically cycles through images in a given directory, selects two, and combines them into one image that can be set as a spanned background image in Ubuntu. The two images are sized proportional to the sizes of your screens so that the combined image fits perfectly to your monitor setup. It can be set as a startup program with a timed slideshow, or used once to generate a single image to use as an unchanging background.

Check out the project site: Dual Monitor Background Switcher