Yeah, that gray linen login screen looked cool when it first appeared in OS X Lion, but honestly? It’s gotten a bit bland. As is typical of Apple, of course, there’s no built in way to change it. We’ve found two ways, one that messes with the system files (you’ve been warned!) and one that uses a third party app to allow us all to have even more pictures of LOLcats on our computers. Or, you know, our kids or pets or something.
Customize Your Login Screen With A Cool New Wallpaper [OS X Tips]