I love Microsoft Teams and I also love controlling my online appearance, but sadly both aren't big friends when you are a Guest in another tenant. There still isn't a good/easy way of controlling your own profile picture, which is sad because you are reduced to a not-very-personal colored circle with initials:
Fellow MVP Kazushi Kamegawa shared a method of changing your profile picture in a private forum, but it stopped working due to some UI changes in the Azure Portal. Luckily, with some more "hackery", we can still make it work!
The tl;dr version:
Tenant switch to the tenant where you want to change your profile picture
Figure out the ID of your user account in that tenant
Open your user profile page in the Azure Portal using a direct link
Edit the profile, upload a profile picture
Wait for about a week to have the profile picture synced into Teams
If you found this blogpost, it's probably safe to assume that you know how to switch tenants. For the purpose of this guide, it is VERY important you do this in your browser because otherwise authentication will get confused ;).
You should now see your profile page in the Azure AD where you are a Guest.
Edit profile and upload picture
Finally time to upload your profile picture!
Top of the profile, click the Edit button
With your profile in edit mode, you can browse for a photo on your computer and upload it to your profile!
Wait and enjoy success
It takes a while for your profile picture to show in Teams, and it might even show for a short while and go away again. But if you have enough patience, after about a week or so, your profile picture should show consistently across the Teams UI both for you and for others!
Until Microsoft Teams or Microsoft 365 gives us an easier way to change our profile picture, this is the best way to do it self service. The days of the anonymous circle with initials are over, time to show your personality also in your Guest tenants!