Samsung
Set a Custom Image on Always On Display auf Samsung
Samsung's Always On Display defaults to a clock face because the photo option is tied to a specific clock style, not to your regular wallpaper. Switching the wallpaper alone has no effect on the lock screen while the display is off, which is why many users assume the feature is missing.
The picture layout lives inside the clock style picker. Selecting a Gallery-based style tells One UI to render your chosen photo above the FaceWidgets area instead of drawing a clock.
To set it, open Tap on Settings ➔ Tap on Lock screen ➔ Tap on Clock style ➔ Tap on Gallery ➔ Tap on Choose from Gallery ➔ Choose an Image/Photo ➔ Tap on Done.
Once confirmed, the image replaces the clock on the Always On Display, and FaceWidgets like battery, date or notifications still show below it.
Bright or busy photos can look washed out on an always-on panel, since the display dims brightness and color depth to save power. If the picture is barely visible, a simpler black-and-white or high-contrast image usually works better than switching back to a standard clock style.