Favorite Lock Screen features:

• Installs your favorite lock/start screen image on Windows 10, or Windows 8.1,
• Installs a randomly selected lock/start screen image each lock/unlock and logon/logoff,
• Supports image file formats: JPG, PNG, GIF and BMP,
• For Windows 10 and 8.1,
• Freeware.

If you enable the Random Image from Folder option the program creates the FavoriteLockScreen task.