I installed Xubuntu 11.10 "Oneiric Ocelot" beta-1 and have been updating it daily since, as of this afternoon. I am able to change the Grub2 background image easily, and also the normal xfce background can be changed easily, including using my own backgrounds.

But the login screen just comes with a solid purple background - very ugly. On other Ubuntu versions, I typically use the "Ubuntu Tweak" program, but that is not available for 11.10, and may not be useful under Xubuntu.

Various system information (which may not be relevant):
Averatec 3280 laptop with 1024x768 screen
Ubuntu version and kernel version
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=11.10
DISTRIB_CODENAME=oneiric
DISTRIB_DESCRIPTION="Ubuntu oneiric (development branch)"
Linux cupid 3.0.0-11-generic #17-Ubuntu SMP Fri Sep 9 17:44:13 UTC 2011 i686 athlon i386 GNU/Linux
model name : Mobile AMD Sempron(tm) Processor 2800+
cpu MHz : 800.000
bogomips : 3207.35
VGA compatible controller: VIA Technologies, Inc. K8M800/K8N800/K8N800A [S3 UniChrome Pro] (rev 01)

Please do NOT respond if your response does not refer specifically to Xubuntu 11.10 beta1 or later, using xfce. Also please make sure you're talking about the login screen, not the Gnome2 boot screen.

I doubt a lot of folks can help you on that yet.

Ubuntu has gone to LightDM (I think that is the name) on all its variations.

If you were using Debian Xfce (I am) I could point you to the config files and the image files.

What I suggest is that you take a look at your /usr/share directory for LightDM (maybe all lower case, maybe I have the name wrong - it is close). This should have the config file to point it to the image. That should have a path. Change the path to the image you want or put your image where the default path leads (changing the name to purplepuke.png or what ever the current image is called).

You may still have gdm3 installed. If so look at /usr/share/gdm/greeter-config for an example of what the dm you are using has to have somewhere.

It turns out that the file to edit is /etc/lightdm/lightdm-gtk-greeter.conf - I changed it as follows:

[greeter]
#background=/usr/share/backgrounds/warty-final-ubuntu.png
background=/usr/share/backgrounds/ocelot.jpg
theme-name=Ambiance

That should look better.

You should mark this solved (under thread tools at top of page).

The next person may run a forum search (hope so) and find this. If it is marked solved they will know it is what they need.

I doubt you will be the last to want to change it.

I also thought that there was supposed to be a gui for lightdm to do things like that.