How to Change Login Picture in MacOS

Step 1: Click the Apple menu in the top left corner and click System Preferences.

Step 2: Click the Apple menu in the top left corner and click System Preferences.

Step 3: Next, click on the profile icon.

Step 4: The pop-up window provides all of the options.

Step 5: When you’ve found an image you like, click it. It will be previewed in the bottom left corner. You can customize some images.
The options to customize are along the top on the right side. For example, for Memoji, you can zoom in using the slider, drag the Memoji around in the circle, choose a Pose, or apply a background color in the Style menu. When you’ve got the login image you want, click Save.

Step 6: Your new login picture will appear next to your name.

Credit : https://www.lifewire.com/how-to-change-your-mac-login-picture-8763026