By default the image on your Google Classroom is a letter to match the first letter of your name. However, what if you want to add your own photo. Note that your Google profile photo IS your Google Classroom profile image. If you change it in Classroom, it will update across Google. Note that the update can take a couple of days to show up across other products.
3 Lines Menu
In the upper left of Google Classroom is 3 lines. Click on this to reveal the sidebar menu.
Go all the way to the bottom of the menu to locate “Settings.”
Click on “Change” next to Profile picture. You can upload your image there. Again, remember that this change may take a couple of days to take effect across all Google products.