How to Change/replace the background image of the MacBook lock screen?

Changing the background image of the MacBook lock screen (login screen) requires a few steps, as macOS doesn’t provide a built-in option to customize it directly. Here’s how you can do it:

Steps to Replace the Lock Screen Background on a MacBook:

1- Locate the Default Lock Screen Image:

• The lock screen background is tied to a system file located in macOS. The file is typically stored at:
  /Library/Desktop Pictures/
• The specific image used for the lock screen might vary depending on your macOS version, but it’s often named something like Monterey.heic, Ventura.heic, or similar (based on your macOS version).

2- Prepare Your New Image:

• Choose the image you want to use as your lock screen background.
• Convert it to a compatible format, preferably .heic (High-Efficiency Image Container), which is what macOS uses for its default images. You can use an image editor like Preview, Photoshop, or an online converter to save it as .heic.
• For best results, match the resolution of your MacBook’s display (e.g., 2560×1600 for a 13-inch MacBook Pro Retina).

3- Backup the Original File:

• Before replacing the system file, make a backup of the original image in case something goes wrong.
• Navigate to /Library/Desktop Pictures/ using Finder (use Command + Shift + G to go to the folder), locate the default image (e.g., Monterey.heic), and copy it to a safe location like your Desktop.

4- Replace the Image:

• Rename your custom image to match the exact name of the default lock screen file (e.g., Monterey.heic or whatever corresponds to your macOS version).
• Move your custom image to /Library/Desktop Pictures/. You’ll need administrative privileges to do this:
  • Drag the file into the folder.
  • Authenticate with your admin password when prompted.
  • If asked, choose to replace the existing file.

5- Disable System Integrity Protection (SIP) Temporarily (if needed):

• macOS protects system files, so if you encounter permission issues, you may need to disable SIP:
  • Restart your Mac and hold Command + R to boot into Recovery Mode.
  • Open Terminal from the Utilities menu and type:
    csrutil disable
  • Restart your Mac, make the changes, then re-enable SIP by repeating the process and typing csrutil enable.

6- Test the Change:

• Lock your Mac (press Control + Command + Q or use the Apple menu > Lock Screen) or log out to see the new lock screen background.

This video describes the process to change macOS Lock Screen image?

Notes:

• The lock screen image is separate from your desktop wallpaper, so this won’t affect your regular background.
• If you update macOS, the system might overwrite your custom image with the default one, requiring you to repeat the process.
• Be cautious when modifying system files—always back up important data beforehand.