Save a picture as wallpaper
- Open Photos & Videos > tap an album > tap a picture.
- If the bar at the top is hidden, tap the picture.
- Tap the More button > Set As Wallpaper.
The message Wallpaper set appears. The picture is scaled and cropped to the screen for you; there is no step to choose the part to use.
Checked against the LuneOS code and installed apps. Nobody has tried these steps by hand yet, so tell us if something differs.