TeamTools uses Gmail pictures for user photos. This is the picture that you see whenever you roll over a name in your Gmail inbox, Contacts, or Chat list.
Any user can change their Gmail picture by going to Settings in Gmail and navigating to the “My picture” section. To ensure the photo appears in TeamTools, make sure that “Visible to everyone” is selected.
G Suite admins can also update user pictures from the Admin console, by navigating to the user and clicking on the picture icon. Google instructions are here.
As with all changes made directly in G Suite, it may take up to 24 hours for the change to appear in the Google APIs and therefore in TeamTools.