Update your user picture using Photo Booth on Mac
Use Photo Booth to update the picture on your card in Contacts and the picture that appears next to your name in the login window on your Mac.
In the Photo Booth app on your Mac, take a photo.
Select the thumbnail of the photo you want to use.
Click the Share button , then choose Change Contact Picture.
Do any of the following to adjust the look of the image:
Adjust the image location: Drag the picture around within the frame.
Zoom in or out: Drag the slider left or right.
You can also change your user picture in Users & Groups settings. See Change your login picture.