To find the location of Windows wallpaper images, open File Explorer and navigate to C:\Windows\Web. There, you’ll find separate folders labeled Wallpaper and Screen. The Screen folder contains images for the Windows 8 and Windows 10 lock screens.
The Wallpaper folder contains additional subfolders listing both the default Windows wallpaper and the wallpaper images that correspond to any installed Themes. For a default Windows 10 Technical Preview installation, for example, you’ll have the default Windows wallpaper in the Windows folder, six images from the flowers theme in the Flowers folder, and four new images from the latest preview build in the Windows Technical Preview folder.