Samsung
Change Wallpaper on Lock Screen auf Samsung
On Samsung phones the lock screen and home screen wallpapers are stored as two separate settings. Changing your home screen background does not automatically update the lock screen, which is why many users end up looking at an outdated photo every time they wake the display.
The wallpaper picker gives you a dedicated Lock screen option that lets you assign a photo only to that screen, independent of your home screen design. You can also select multiple images at once, so the system rotates through them each time the screen turns on instead of showing a single static picture.
Where the setting lives
Open Tap on Settings ➔ Tap on Wallpaper ➔ Tap on Gallery ➔ Select a Photo/Image ➔ Tap on Done ➔ Tap on Lock screen. Confirming with Lock screen instead of Home screen is the step that most users skip, which is why the change does not seem to apply.
If you only want to update the home screen background, choose Home screen at the same step instead. Both wallpapers can also be set to the same image from this menu if you prefer a matching look.