Changing Greeter Background Image

[Basil L. Copeland Jr.]

I'm trying to change the greeter background image.  I've tried using the GUI login screen tool to shift from the Graphical greeter to the Standard greeter.  The GUI tool shows the Standard greeter pointing to the image I want for my background.   But I still get the Bluecurve background.   I've tinkered with gdm.conf.   But I still get the Bluecurve background.   So I've delved into GdmGreeterTheme.desktop Bluecurve and pointed "screenshot=" to the image I want to use.   I still get the Bluecurve background.   What do I have to do to modify the greeter background?