Wallpaper Cycler Lite
If you have hundreds of image files on your hard drive, and want to be able to use all of them as desktop wallpaper, then Wallpaper Cycler Lite is what you need.
With this powerful program you organize your wallpaper files into categories, then set each category to display at various time intervals or even according to the season. You can also create slide shows.
However, the program is very challenging to use, even with the detailed Help system, Quick Start tutorial, Basics of Wallpaper Cycler guide, and Add New Wallpapers wizard. I spent almost an hour setting up the program to test it, and still couldn't figure out how to use most of its features.
That said, Wallpaper Cycler Lite is free. If you have an enormous library of images that you'd like to display, it may well be worth your time to give it a try.
If this free version doesn't have enough features for you, go to the vendor's site to try the $20 full version--which can display live Webcam feeds, among other functions.