I have a service running that renders a changing wallpaper every 5 minutes or so, and replaces the current image file with the new one automatically (That is to say, new image but same filename). On Linux, the change is detected almost automatically, and so I have the most current wallpaper. However, on my Windows 7 machine (Which syncs the image with my Linux machine over Dropbox), it appears to cache the wallpaper from the last time I manually set the wallpaper. The image never changes, even if I restart.

Is there a way to make Windows detect the file change, or periodically refresh the wallpaper cache? I'd like to avoid third-party apps if at all possible.