There is a bug in the current release of the GDM (Linux) Screensaver and it shows ONLY the default background. Not the current one like it is supposed to.
The hack for this is to copy what you want to the following file:
/usr/share/pixmaps/backgrounds/gnome/background-default.jpg
at least that is what the page below says.
Arch Linux Forums / Lock screen?
That did not work on my Ubutntu based retool, EasyPeasy.
For Easy Peasy the following worked
root@host:/usr/share/gdm/themes/SleekDragon# cp /usr/share/backgrounds/easy-peasy-4.png /usr/share/backgrounds/easy-peasy-4-save.png
root@host:/usr/share/gdm/themes/SleekDragon# cp Sleek_and_Sporty.png /usr/share/backgrounds/easy-peasy-4.png
The whole reason that I wanted this change is that the Easy Peasy logo is horrible. I like most of their work, but the graphics just don’t work for me.