It seems that currently there is no way to configure simple locker's background. It always shows the same picture. I think, using user's wallpaper is better. This way simple locker can be kept "simple", but gain some configurability. Reproducible: Always Steps to Reproduce: Lock screen with simple locker Actual Results: Locker always uses the same picture as background Expected Results: My desktop's wallpaper used as background
Simple Locker is either not a KDE product, or is abandoned. We use KScreenlocker now, which has configurable backgrounds.