Change Ubuntu Login Screen
One of the joys of using Ubuntu is the ability to easily customize even the most obscure features of the operating system and the login screen included with the default GDM theme is no exception. As with most light Linux tweaks, this one is quite straight-forward.
There is a utility included with Ubuntu that allows quick and easy customization of options within the GDM theme titled gdmsetup; you can run this utility directly from the main menu by looking under System -> Admin -> Login Window.
You’ll need to enter your admin password to gain access, then click on the tab labeled “Local” to see theme options. Under the section labelled “Style” you can select one of three main presets: Plain, Themed or Face Browser. Select “Themed” to gain the ability to select any graphic you like from the provided list along with several other default GNOME themes that may suit your fancy – customization is always great but you have to admit that the default GDM theme is a pretty attractive piece!