GDM background image

[Jeff Hornsberger]

Hi, I'm looking for a way to set the background image for gdm. I know it
is set in /etc/gdm/Init/Default using xsetroot, but I want to set it to
an image not a color. As far as images goes xsetroot apparently can only
handle bitmaps, my question is: How do I set the background of gdm to a
jpg (or some other common image format)? Thanks. -Jeff