How to use Windows Configuration Designer to set desktop wallpaper

I'm using Windows Configuration Designer to provision new company laptops, the documentation is vague on how to properly set the Personalization settings to set the wallpaper.

I have my jpg file, I've set the path to it locally under the DeployDesktopImage field, and then set DesktopImageUrl to the filename (as my best interpretation of the directions) but it fails. Does anyone know what the right way to do this without using a URL to a hosted web image is?