Change your login screen photo
When you log in or switch users, you will see a list of users with their login photos. You can change your photo to a stock image or an image of your own. You can even take a new login photo with your webcam.
You needto edit user accounts other than your own.
Open the Activities overview and start typing Users.
Click Users to open the panel.
If you want to edit a user other than yourself, press Unlock in the top right corner and type in your password when prompted. Choose the user from Other Users.
Click the pencil icon next to your name. A drop-down gallery will be shown with some stock login photos. If you like one of them, click it to use it for yourself.
If you would rather use a picture you already have on your computer, click Select a file….
If you have a webcam, you can take a new login photo right now by clicking Take a picture…. Take your picture, then move and resize the square outline to crop out the parts you do not want. If you do not like the picture you took, click Take Another Picture to try again, or Cancel to give up.