A profile picture on a Mac is also called a user picture. It appears when you sign in to your Mac account and when you use the iChat and Address Book applications. Typically, a profile picture is installed the first time you set up your Mac, but you can change it in System Preferences.
Steps
Part 1 of 3: How to Access Your Profile Picture
Step 1. Open the Apple menu
And then click System Preferences> Users & Groups.
Step 2. Log in as an administrator
First, click on the padlock icon and then enter your administrator name and password.
Step 3. Select the user account whose image you want to change
Click on the picture. A menu will open where you can select the image source.
In addition, you can now simply drag the image into the user account window
Part 2 of 3: How to choose an image source
Step 1. Select an image category
The categories are Default (images that come preinstalled in OS X), Recent (images you recently used), and Linked (images from your contacts). You can also select "Faces" for the system to automatically detect and extract faces from saved images. Select iCloud Photos to use the image you uploaded to iCloud. To use a photo taken with a webcam, go to the next section.
Activate iCloud Photo Library before using it as a source of images. To do this, open the Apple menu and click System Preferences> iCloud> Preferences (next to Photos)> iCloud Photo Library
Step 2. Click "Change" on the button below the image
This will enlarge and crop it.
Step 3. Tap on the desired photo and then tap "Done"
The profile picture will change.
Part 3 of 3: How to use the webcam image
Step 1. Click "Camera"
This option is in the menu that opens if you click on the current user image; you will find other sources of images in the same menu.
Step 2. Press the shutter button that appears
A camera built-in or connected to a computer will take a photo after a three-second delay.
Step 3. Click "Change" below the image
Cut it off as needed.
Step 4. Click Finish
The profile picture will change.