On Bing's homepage, there is a download button that can be use to download their images for free, for you to keep. The only catch to that is that you have to connect your Facebook account. If you have no issue doing this, then I'll show you how to quickly connect your Facebook account to Bing if you haven't done so already, and then you'll be able to download the wallpaper using the download button.
- Go to the Bing Homepage
- Click Connect now or you can sign in via clicking the download button on the page. You can also use the sign in link at the top right
- Download your wallpaper.
After connecting the download button is located at the bottom right, near the bottom of the page. They look like the second image to the top right -- all the way on the right.
If you don't have a Facebook, don't worry. If you use IE8 I already have a tutorial out for you for how you can get around this.