Rafael has done it again. And this is the perfect time to remind people that there is a huge difference between finding something that's right there in the UI (as some have done with previous builds and tried to take credit for a "discovery") and delving into the underpinnings of the OS and making actual discoveries. This is the latter kind of discovery. The real kind.
As you probably know, Windows 7 build 7057, a build recently leaked to the public, sports a new (yet ugly) login UI background. Delivering on the “more customizable” promise, Windows 7 now supports the ability to load images into the background of the login screen without the use of third-party software or manual hacks.
Although this functionality was designed with OEMs in mind, it is pretty easy to turn on and off using regedit and some images lying around your hard drive.
Good stuff, as usual.