Comment 1 for bug 1622988

Hello, I have the solution:

1) In ~/.local/share/ create a folder named "backgrounds" (no quotes)
2) Set the permissions on this folder to 600, or 644
3) Try again in the System setting, but now use the dropdown menu "Custom"

Blank screen again?

1) Try looking in the previus "backgrounds" folder if the files (automatic copies of the original images) have the 600 or 644 permission.
2) If have, but doesn't work, set the permissions to 700.

Blank screen agaaain?

try a reboot and tell me whats is the matter now.