For the beauty of a system you can placed your current background for your Kscreensaver instead of the default.
KDE is by default not able to changes this for the ‘Simple Lock’, see in this open bug for more Info.
But there is a a small workaround for this.
Change into the
/usr/share/apps/ksmserver/screenlocker/org.kde.passworddialog/contents/ui/ directory and edit the
main.qml with your editor of your choice.
Create a backup of this file,
cp main.qml main.qml.baku
then edit on the line 45 and replace:
- source: theme.wallpaperPathForSize(parent.width, parent.height) + source: "1920x1080.jpg"
Now you copy your current background image to
Note you have to redo this for each update of the package “kdebase-workspace”.