Comment 3 for bug 918617

I think it is unfortunate that, while many design tweaks are made an the GUI gets a lot of attention from Canonical, this bug seems to remain unresolved. Not the least because users get mixed feedback (setting the desktop wallpaper to one image changes that of the login screen as well, but for the 'slideshow' this doesn't work).

If you don't want the default background of unity greeter, and you want a dynamic/slideshow background for you desktop, you may find a temporary and local fix here: http://askubuntu.com/questions/64001/how-do-i-change-the-wallpaper-in-lightdm/64002#64002