Jeffrey found this link.
Many of the wallpaper images included with Windows Vista were generated by amateur photographers, with a large number being sourced through flickr. I presume, like so many other image buyers trolling flickr, that they didn’t pay the photographers, and instead just offered them the glory of being included in Vista. Why? Because licensing costs for image reproduction and worldwide rights for many years is expensive.
So, is the Microsoft cheap, or are the existing licensing models inappropriate for this type of usage?