Since Ubuntu 13.04, in my laptop, when I choose an image as desktop background from my pictures folder, the login screen remains as the default purple image. To solve that I had to add the image I wanted to /usr/share/backgrounds.
Later on, I upgraded to Ubuntu 13.10, and the same thing happened. But then, one day I installed Ubuntu 13.10 in another computer, and I realized that when I chose an image from the pictures folder as desktop background, the image appeared in the login screen. So how is this possible? Is it because I upgraded from 13.04 to 13.10 in my laptop, and the one in the other computer was a fresh installation of 13.10? And, what can I do to fix this?