Custom Login Screen
In Tech Tails past I have written about ways to change the image behind the login window. In Tiger, Leopard, and Snow Leopard, there was an image in the Core Services folder called DefaultDesktop. This was the image displayed both behind the login window and as the systems default desktop after logging in. Those rules no longer apply as Apple has made changes to the default desktop in Lion and Snow Lion.
The brushed metal background that is a unifying theme across the desktop and iOS operating environment is contained in System Folder much like DefaultDesktop was. The location and format has changed, though. The image is a PNG (portable network graphic) and is named NSTexturedFullScreenBackgroundColor.png. The file itself is located in a resources folder buried deep in the System.
The exact path to this folder is as follows: /System/Library/Frameworks/AppKit.framework/Version/C/Resources.
To change the background, you’ll first want to find a file of equal size to the the default resolution of your computer. (You can also use a 256 × 256 pattern and it will tile the entire space.) The image will have to be opened in Preview and saved as a PNG. The DefaultDesktop in systems prior to Lion was a JPG file. You will then need to rename the new file “NSTexturedFullScreenBackgroundColor.png”.
Navigate to the resources folder and first make a copy of the default that already exists. You may want to move the duplicate to another folder for safe keeping. Drag and drop your new image into the resources folder. The Finder will ask if you want to replace the existing item and you’ll be asked to authenticate to make changes to the System folder.
After logging out or restarting, the new image should become the background for the login window and the wallpaper behind Mission Control as well as Dashboard.