For the Upload image option, an image preview is always shown. It is saved in the policy and available during subsequent editing of the wallpaper.
For the Download image from internet option, the Preview button appears if the image is downloaded from a URL beginning with http://. Click the button to show an image preview. The preview is not saved in the policy. That means you may need to re-download the preview after editing the wallpaper.
The Preview functionality does not work for images downloaded from URLs beginning with https://.
If you want to use the same image as a wallpaper for a lock screen, select the Use the same image for lock screen check box. Otherwise, the image is used only as a home screen wallpaper.
The check box is cleared by default.
Click the OK button to save the changes you have made.
The imported image is set as a wallpaper on users' devices.