Mac login window tricks, Part 4: Change default background image

The fourth and final segment of MacYourself’s Mac login window tricks series helps make your Mac your own. Ditch the login screen’s default background in favor of a custom image of your choice.

One of the first things many people do when they get a new computer is change the desktop background image, also commonly referred to as wallpaper. It’s a mundane task, but it’s one people do to make the system truly theirs. Out goes Leopard’s sci-fi space photo and in comes your favorite athlete, family member, or landscape. What you may have noticed, however, is that Leopard’s default wallpaper isn’t totally gone.

Upon booting a Mac, the background you see behind the login window is still the purpley-pinkish star image Apple ships with Leopard, even though you changed the background to something else in your user profile. It turns out you need to do some tweaking if you want a custom image to display here, so let’s get to it!

First, you will need a quality image file to use as your login screen background. The higher resolution, the better. Next, place the file in your user’s Public folder (Macintosh HD > Users > [Username] > Public). The reason why it’s a good idea to stick the file here is because it needs to be in a location that is accessible to all users, and this is the easiest way to go about doing so. Now it’s time to venture into Terminal (Applications > Utilities) and take a look at this command:

sudo defaults write /Library/Preferences/com.apple.loginwindow DesktopPicture /Users/Username/Public/custom_background.jpg

Before copying and pasting this into Terminal, we should go over a few important things. Most of the command is identical to the ones we’ve been using for the previous three parts of this series, so I won’t go into detail about it yet again. It is worth mentioning, though, that DesktopPicture is the parameter we’re creating in the preferences file that tells the operating system where to find your custom wallpaper.

As you might have guessed, the part at the end is the file path to your new background image. You will need to make some modifications — specifically, replacing “Username” with your actual username and changing “custom_background.jpg” to the name of your file. Once you have done that, you can bring the command into Terminal and press Enter/Return. Type your password if prompted, quit Terminal, and log out to see your results.

With any luck, there will be no more space theme! Although, I have to admit I’ve grown fond of Leopard’s default background and decided to keep it myself. My MacBook Pro just didn’t look right without it. If you’re in the same boat and want to revert back to the Apple-provided image, run the following command in Terminal:

sudo defaults delete /Library/Preferences/com.apple.loginwindow DesktopPicture

For more Mac login window tricks and tips, check out the other segments of this 4-part series: “Mac login window tricks, Part 1: Unleash hidden system information“, “Mac login window tricks, Part 2: Add a custom welcome message“, and “Mac login window tricks, Part 3: Hide certain user accounts“.