Sent Images show has question mark iMessage

Why do the pictures I send from my iPhone to other peoples iPhones via iMessage show up as a thumbnail with a question mark and I can’t see the picture? It happens when I send pictures to my friends then when I go back to check I don’t remember what pictures I sent because I can’t see them anymore. It’s very frustrating when I need to go back to check what I sent others for projects at what not…not sure if this is any help but it doesn’t happen all the time. It will happen randomly. I send other people the same photos and their messages show the photo I sent but the same photo won’t show the photo I sent for another person. Also it shows the actual photo initially but disappears a couple days later and just shows white box and question mark when I check chat history. See example below sent image showing as a box with question mark