You can use John's Background Switcher from the command line. If you don't like having it running in the background all the time (even though it doesn't consume many resources) then you can still change your background periodically by running it with the one of the following command line arguments:
BackgroundSwitcher.exe [/next] [/previous] [/refresh] [/shuffle] [/gotocurrent] [/switchto [center|stretch|scale|overscale] "c:\photo.jpg"] [x]
- /next - Selects the next background
- /previous - Reverts to the previous background
- /refresh - Redraws the current background
- /shuffle - Shuffles the backgrounds if you have multiple monitors
- /gotocurrent - Browses to the currently displayed background(s)
- /switchto - center|stretch|scale|overscale "c:\photo.jpg" x - Switches the background to the specified photo in the specified mode (choose one of center, stretch, scale or overscale). If you have multiple monitors you can optionally pass in the monitor number for x (1 for the primary, 2 for the secondary and so forth)
You can use the /? command line switch to display the currently available command line options.
Note that if John's Background Switcher is already running then only the /? and /switchto command line options will work.