Is it possible for someone else to intercept a text message I am sending and add a photo to that message? I recently answered a text message I received from a friend and half way through typing out the reply, an old intimate photograph of me inserted itself into the body of the text message. Can this be done by someone else i.e. an ex who may have someone put spyware on my phone and whilst monitoring my text messages has decided to add this photo? Is there anything out there that is capable of this?
That would require the connection or receiving app to be compromised, the former an unlikely premise for a modern app using AES, like Google Hangouts or Telegram and I don't believe that rootless apps can manipulate other app content.
In short, yes, it is possible, but if you use a modern, secure app (and don't let your ex use your phone), it can only be from a selfrooted spyware app.
EDIT (questions from comments, until i can comment): @Steve SMS does not support photos. MMS is a viable attack vector, as it is not often encrypted. As such, migration to an AES encrypted message app is recommended.
@Neil App verification can be completed through secure hash and comparison with a known good copy.