Background image:
You can change the background image of the Login Window.
Select: This button allows you to choose a replacement image for the background of the Login Window. By default, the application directs you to the folder containing the Desktop Pictures of Mac OS X (/Library/Desktop Pictures/...). You can choose another image but it must be accessible by all users, for example in the Public, Shared or Sites folder.
Formats accepted: PNG, JPEG, JPEG-2000, GIF, PSD, TIFF, TGA, BMP.
Restore: This option allows you to put the original background image in the Login Window.