Change the Login Screen Wallpaper in OS X Lion

NOTE: New instructions are available to change the login screen background image within OS X Mavericks. Please refer to those if you are looking to customize the login wallpaper in the latest versions of OS X.

Here’s how to change the wallpaper that lies behind the standard login screen on OS X Lion & Mountain Lion (although not the login background you see if you have FileVault enabled, which cannot be altered). As such, this tweak is not for the fainthearted because it involves editing system files and will therefore affect all users of the system. Previous tips here at OSXDaily have explained how to change the login screen background in prior versions of OS X, but OS X Lion and OS X Mountain Lion changed everything (again).

For OS X Lion & Mountain Lion, the file we need to replace is called NSTexturedFullScreenBackgroundColor.png and is located at:

/System/Library/Frameworks/AppKit.framework/Versions/C/Resources/

As with the Mission Control and Dashboard wallpapers, the login screen wallpaper is actually a pattern that’s repeated from left to right, top to bottom. You can replace it with a similar pattern of the same size (256 x 256 pixels) or use a full-size image the exact same resolution as your monitor.

Note that because the white text and graphics of the login screen are overlaid on the wallpaper, darker wallpapers tend to work better than light ones.

How to Replace the Login Screen Wallpaper in Mac OS X Lion

1. Open the image you’d like to use for the wallpaper in Preview and convert it to PNG format by clicking File -> Export. In the dialog box that appears, select PNG from the Format dropdown list and change the filename so it reads “NSTexturedFullScreenBackgroundColor.png”.
2. Back up the original wallpaper image by opening a Finder window, hitting Shift+Command+G and typing the following path:

/System/Library/Frameworks/AppKit.framework/Versions/C/Resources/

3. Now copy the “NSTexturedFullScreenBackgroundColor.png” file to a safe backup location.
4. Then click and drag your new image onto the Finder window so it overwrites the original. You’ll be asked to authenticate, so click the button in the dialog box that appears and type your login password when prompted. Choose to replace the original file when prompted.

That’s all that’s required, but you’ll have to reboot your computer for the change to take effect.

If you find the wallpaper pattern shrunk and repeated across the login screen rather than filling it, try using an image editor to create a new image of the same resolution as your screen (that is, 1280 x 800, for example), and then open your wallpaper image before copying and pasting it into the new image. Then save out the new image to the location mentioned earlier using the filename that’s mentioned.

To revert to the default login wallpaper, repeat the steps above to browse back to:

/System/Library/Frameworks/AppKit.framework/Versions/C/Resources/

And drop your backup “NSTexturedFullScreenBackgroundColor.png” image back in place.

This is another tip from Keir Thomas, author of Mac Kung Fu, a new book with over 300 tips, tricks, hints and hacks for Mac OS X Lion. It’s available from Amazon, and also in eBook form for all eReader devices, including Kindle.