Gordon is saving the daily images for both Bing US (United States) and Bing DE (Germany) in two separate galleries using a modified script. Click below images for each gallery.
These background images aren’t the correct size to be ideal for desktop wallpaper, you could use Stretch, Screen Fit options in Display properties.
Also, Bing Image Archive from istartedsomething.com is excellent calendar listed with each day background image. Save from here.
Bing Downloader is a small 10KB application that can download images from Bing.com and store in your local PC. This has to executed everyday. The app requires .NET Framework 3.5.