Create a fluid transition from login window to desktop in two easy steps

As of Snow Leopard 10.6.x you can change the background image easily by navigating to Finder -> "Macintosh HD" -> System -> Library -> Core Services -> DefaultDesktop.jpg

This is for those who don't want to download additional software onto their computer to accomplish this.

Great article - I'd love to see something on how to enable the transition effect!

FYI: this doesn't support Snow Leopard Server but I can handle that.

Here's another wallpaper you guys might like :)

http://jarin.posterous.com/one-of-my-favorite-christmas-desktop-wallpape

It has always amazed me how haphazard the Mac startup background is since Leopard. A grey screen, two shades of blue, a star field and then your desktop background. Come on Apple you can do better!

I put a graphically intensive Quartz composition on there instead of an image. The smell of burning PCB is festive!

I found this just works without sudo:

defaults write /Library/Preferences/com.apple.loginwindow DesktopPicture ~/Pictures/Desktop.jpeg

I made Desktop.jpeg a symlink, then set both wallpapers to that symlink, now I can change both wallpapers by just changing the symlink.

Um, this functionality has been in the OS forever. Sorry to burst your bubble, but you don't need a third-party app. Simply fire up Terminal and enter the following line:

sudo defaults write /Library/Preferences/com.apple.loginwindow DesktopPicture /path/to/image.jpg

That will have the same effect. I fail to see how that's "the hard way" when the alternative is downloading a third-party app and running it. Seriously. One line. You can even drag the image into the Terminal window instead of typing out the path.

@kud you win...

The login window background is located in the following folder:
/System/Library/CoreServices

under...

DefaultDesktop.jpg

If you want to replace it, ensure the background you want to use is:
in .jpg format
same resolution as your desktop background (System Preferences/Displays)

It will ask you if you want to replace the current file, click on Replace.

You will need to have admin access.

I would recommend making a copy the file before replacing it in case you don't like how it looks.

so good to see there's a free app to do this. i'd done this before on my old powerbook using terminal. one question though; you say "the login box would fade away...", but mine doesn't. the whole screen rotates to the right (with login box). am i missing something here or am am i just taking your words too literally? perhaps there's a setting to change the rotating to fading?