From Hongsong Li:
Beautiful Pictures Free app automatically downloads beautiful background pictures from Bing home page to your machine. And you can set them as the background of your lock screen. This app will check more than 40 Bing homepages for different countries and only download new pictures. Since the background picture of Bing home page varies for different countries and changes everyday, you can get very beautiful new pictures. Newly downloaded pictures will be sent to the live tile of this app. You can Browse downloaded pictures, and set one of them as the background of your lock screen.