Spews stands for Simple Process Excluding Wallpaper Switcher and is designed to automatically switch your wallpapers on a configurable schedule. Add your image folders, choose your wallpaper options and click the enable button at the bottom. You can check/uncheck the images paths as needed; only checked paths will be scanned for images.
Spews also has a feature that automatically suspends the wallpaper switching if it detects any process names you configure in the exclusions section. This can be beneficial, for instance, when running games whose graphics corrupt if the wallpaper is changed.