Easier.
Just add this code to any client script:
sw, sh = guiGetScreenSize ( )
width, height = guiGetSize ( IMAGEPATH ) --IMAGEPATH is the path of the logo (e.g. "logo.png")
guiCreateStaticImage ( sw - ( width / 2 ), sh - ( height / 2 ) , width, height, false )
and create a meta.xml that includes that file.