I have an application that successfully gets the users photo using a Microsoft graph API call.
https://graph.microsoft.com/v1.0/users/<upn>/photos/48x48/$value
For some users, that API call will return a 'not found' error. However when looking up their profile in Azure AD, a photo is available there. Their photos are also available in other apps like Outlook, Skype, etc.
Where does Microsoft graph look for user profile photos?
The photo is retrieved from Exchange Online profile photo store. This is used by the majority of services now across Office 365. This photo is updated by going to Delve, Teams and a few other places.
In some cases, depending on your configuration (on-premises hybrid scenarios) this gets a little more complicated. In those scenarios, you need to ensure that Azure AD on-premises is syncing photos that are uploaded to other stores.
There are some solutions out there, including one by Hyperfish as an example https://blog.hyperfish.com/importing-and-exporting-photos
