delete picture from Teams conversation.

Hi

An external users send a picture in Teams conversation to an internal user. Any suggestions??

What I have tried

1. There is no delete chat option in the chat conversation. 
2. I removed the user from teams onedrive hold policy, its been a week. 
3. There is no delete option on the actual picture
4. Ran a content search, verified the picture is in one of the messages, ran purge hard delete. 
5. opened the meeting series and joined the meeting to see if the external could view and delete the photo. It turns out that the external can't see the photo in the chat history therefore, he's unable to delete it.