Comment 19 for bug 844081

The implementation we are aiming for is to have the image stored by the accounts service in the same way that the face image is. We don't want to access the user's home directory directly as it may not be available until authentication has been completed. This has the same limitation of potential offensiveness (you can always set your face image to something offensive) but it also means that the background is volunteered by the session to be shown in the greeter. If a session does not provide a background then the default will be shown. In Ubuntu the default behaviour will have the background updated in accounts service each time it is changed in gnome-control-center. As Mark said an option to disable this would probably doesn't seem worth adding to the GUI, but I would add a GSettings key to disable this and this could be exposed in a tool like Gnome Tweak Tool or Ubuntu Tweak.