This wallpaper changer will monitor your chosen folder and recognize when new pictures are added or old pictures are removed. It will also recursively drill down through each subsequent folder checking for images. You can also set how often it rotates the images from 1 minute to multiple days.
Other feature include setting program to start with windows and a progress bar to show when the next wallpaper change will take place.

Features
Folder Monitoring
Auto Start
Recursive folder search
Change Desktop color to match image color
Rotate wallpaper every N length of time
Progress bar displays when next change will take place