Custom desktop wallpaper isn't displayed in the greeter (12.4)

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Status changed to 'Confirmed' because the bug affects multiple users.

Well, to get your personnal images displayed in lightdm, you have to copy them to

/usr/share/backgrounds

And you have to create or modify the file

personnal-wallpapers.xml

located in

/usr/share/gnome-background-properties

keeping this in mind :

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE wallpapers SYSTEM "gnome-wp-list.dtd">
<wallpapers>
  <wallpaper>
    <name>my_personnal_picture_01</name>
    <filename>/usr/share/backgrounds/my_personnal_picture_01.zyx</filename>
    <options>zoom</options>
    <pcolor>#2c001e</pcolor>
    <scolor>#2c001e</scolor>
    <shade_type>solid</shade_type>
  </wallpaper>
  <wallpaper>
    <name>my_personnal_picture_02</name>
    <filename>/usr/share/backgrounds/my_personnal_picture_02.wvu</filename>
    <options>zoom</options>
    <pcolor>#2c001e</pcolor>
    <scolor>#2c001e</scolor>
    <shade_type>solid</shade_type>
  </wallpaper>
</wallpapers>

If you remove the line <options>...</options> you'll be prompted when setting your wallpaper what kind of display-mode you want to use (zoom, span, fill...)

The color here is a a very dark pink, almost black.

An easier, transparent or automatic way of doing that would be indeed very nice !