One of the first things I changed after installing Leopard was the desktop picture. Not that I wanted to customize my computer, give it a personal touch, but i hated this space-timemaschine-pink-horror.

But until now there was still this well-known picture at the Login In Screen.
Here is how you also can remove this:

Go to /System/Library/CoreServices/
You will find there a picture called DefaultDesktop.jpg

copy this file to your documents folder or whereever you like to back it up and rename it.
Go to your favorite image processing application and create a new picture

Name this picture DefaultDesktop.jpg and copy it to the CoreServices Folder.

You may have to change the sharing rights of the original file. So hit command+i to get the information panel and add your account name. You will have to know your admin password!

That’s it!