Where are hidden photos stored from a gmail account?

[AC Question]

Over a year ago I attached some photos to a text. I thought they had been deleted by the recipient. Now I learn that the photos reappeared on his new wife's phone after she bought a new phone and the two synced theirs phones. There is not an option to delete them. Where are these photos being stored? I think they originally were sent to a gmail account but he can not access the account because he forgot the password. We all just want the photos deleted permanently. Any help would be greatly appreciated.