Just what I did, the backgrounds are ones I have saved
from many versions of back distros backgrounds and I
have put them in the folder for the backgrounds. In
Xubuntu they are in a folder called backdrops but still
the one the system uses. When doing as you say below they
don't even show up to select, just he ones delivered with
the system.

Still trying. Looking as permissions doesn't make sense.
I even tried to redirect to another folder of my pictures.