Microsoft has a new app that sets the "daily Bing background image" as your desktop background image and updates it every day:
If anyone chooses to install it, I strongly recommend unchecking
"set Bing as my homepage" and "set Bing as my default search provider" during the installation process.
I installed it. It lets me choose from the past week of Bing background images.
I just installed it today, so I don't know if I keep the images once they are on my computer, or if I am limited to only the most recent week of images. I'll know tomorrow if the oldest image gets dropped from the lineup.
The few copyrighted background images (the ones that Bing has always prevented people from downloading) have a different image substituted in the lineup of the app. The substitute images are nice too though.