If you are tired of the same old login screen on Facebook, and if you want to customize it just like the desktop of your computer, then you must try this extension for Google Chrome that lets you change the background image at the login to Facebook.

Once you've installed the extension (from here), go to the list of extensions (the wrench at the top right, tools, extensions), try FB Login Screen Changer and click on "Options".
You can enter the URL of the background choice and set whether to repeat horizontally or vertically.

At this point, after logging out of Facebook, visiting the site you should display your background image.