Apple's standard lock-screen image with OS X El Capitan (and Yosemite before it) is a blurred version of your desktop wallpaper. If you have grown tired of this look, then you can add your own wallpaper. You can also add a message to your lock screen, which can add a bit of fun, motivation or information to your Mac after you log out. Lastly, you can change the user icon for your account and any other accounts you have set up on your Mac. Let's dive in.
1. Add your own lock-screen wallpaper
For best results, you'll want to find an image that is the same resolution as your Mac's display or resize a larger image to your Mac's resolution. To check the resolution of your display, click the Apple button in the top-left corner and choose About This Mac. Your Mac's resolution is listed on the Displays tab.
After you find and download an image you want to use, you'll need to convert it to a PNG file format. To do so, open Preview and go to File > Save As. First, choose PNG from the Format menu at the bottom of the window. Then at the top, give the file this name: com.apple.desktop.admin. The resulting file name must be exactly as follows:
With your file ready, open Finder and go to Go > Go to Folder. In the pop-up window, enter /Library/Caches and click Go. This opens the Caches folder. You will already have a file with the above name that OS X uses for your lock-screen wallpaper. Drag your image into the Caches folder and click Replace.
Now, the next time you log out, you will see your custom wallpaper. If you change your desktop wallpaper, however, OS X will replace your custom image with the standard, blurred version of whatever you chose for your new desktop wallpaper.
Although you will erase your sweet custom lock-screen wallpaper when you choose a new desktop wallpaper, it does mean that you don't need to bother with backing up the default file in the Cache folder when you replace it with your own image because OS X adds a new file to the Cache folder each time you choose a new desktop wallpaper.
2. Add a message
Add a bit of wit, whimsy or information to your lock screen by penning a message.
- Open System Preferences and click Security & Privacy
- Click the lock in lower-left corner and enter your password to make changes
- Check the box for Show a message when the screen is locked
- Click the Set Lock Message button
- Write your witty, sarcastic or informative message and click OK
Your message will appear toward the bottom of the lock screen, just above the Sleep, Restart and Shut Down buttons.
3. Change the user icons
You can change the stock icon that Apple chose for your user account.
- Open System Preferences and click Users & Groups
- Mouse over the current icon and click edit.
- Choose a new image or snap a shot using your Mac's webcam.
- Click Done to save the new image
To change the icon of any of the other user accounts you have set up, you need to click the lock and enter your password before following the same procedure.