It sure seems to me like people are just using email to share pictures (licenses, legal docs, as well as pictures of the kids.)
Are these messages that are being sent by individuals from their phones? Or is there some program that is sending these?I can see it being too much work to type a subject if you are just texting a snapshot to someone else on another phone, but if it is a program, perhaps it could be trained to put a "Here is your photo!" subject in the mail and eliminate the problem.