Dynamic theme is a free Windows 10 app which enables using Bing or Windows Spotlight images as desktop wallpaper, on the Windows Lock Screen, and more.
A familiar interface looks much like any other Windows 10 settings page. A left-hand sidebar lists the main function areas - "Background", "Lock screen", "Daily Bing image", "Daily Windows Spotlight image" - and clicking any of these displays related options.
Selecting "Background", for instance, enables setting your desktop wallpaper to the latest Bing or Windows Spotlight image (it updates automatically); a single Bing or Spotlight image (it stays on that picture until you decide otherwise); any single image on your PC, or a slideshow of images from your PC.
The "Lock Screen" area gives you precisely the same choices for your lock screen.
The program can collect Bing and Windows Spotlight images, save them locally, display a preview when new images arrive, even use the latest image as the dynamic tile of an application.
Not interested in some of these features? No problem, they're all turned off by default. You could use the app just to set your background, or click Bing images, if you like, or you could enable absolutely everything: it's your call.