Office 365 administrators can update Azure AD guest accounts with photos. Guests can do the job themselves using three PowerShell commands. Other approaches work too, but this is the easiest and quickest method to do the job, especially if you have guest accounts in multiple tenants.
Recent developments sees the ability to stop Teams users updating their photos by enforcing controls in OWA mailbox policies. Organizers can stop Teams meetings without waiting for everyone to leave with a new End meeting option in the meeting menu. Both changes are rolling out.