How to change the lock screen wallpaper in Debian 10 with the budgie DE

I’m running Debian 10 with budgie and lightdm slick greeter.
I figured out how to change the login screen. (by manually changing it in /etc/lightdm/slick-greeter.conf )
but I can’t change the lock screen wallpaper.
changing it in the settings doesn’t work (it works in solus).
I’ve tried lightdm-gtk-settings with no luck.

I would appreciated if you can help me. and I know DMs are probably not the best way to getting help but I don’t know where else.

Its gnome-screensaver that is the lock screen.

Now under ubuntu I patched gnome-screensaver to integrate with budgie. The dconf key for the gnome-screensaver wallpaper is served by this example path, key and value

org.gnome.desktop.screensaver picture-uri=‘file:///usr/share/backgrounds/budgie/ubuntu_budgie_wallpaper1.jpg’

I know it’s gnome-screensaver (where as solus uses a fork called budgie-screensaver downstream).
I tried what you suggested but it didn’t work. the value is changed but it would use the default.
I tried using a png image and jpg image it doesn’t make a difference.
and yeah, I’m planning on switching to UB with the release of the LTS (20.04)

yep - concur - I’ve had a fiddle on debian 10 and couldnt change it.

I’ve also looked at the gnome-screensaver source code but couldnt find out how Debian’s version manages the background picture - oddly it does seem to be rather hard-coded.