Originally posted by: Lord Evermore
Assuming you use Windows, use the slideshow screensaver, and make your desktop's image the only one in the folder. If you actually want it showing icons and everything, you'd have to make a screenshot of it. As far as I know there's no way to lock the machine and still show the desktop (unplug the keyboard and mouse would work 🙂).
Of course you ought to be letting the monitor go to sleep anyway.