@: no, /usr/share/backgrounds just have wallpapers in GNOME, not KDE.
And I use dolphin, but when I press Alt+, no happen. ! In Dolphin, there is an option that show hidden file, but not show hidden folder, so I cannot see .kde folder.
Please help me how to solve this. (or just tell me how to take wallpapers here). I think this work seems easy, but I cannot find on Google