How to tell whether the information sent by iPhone is MMS or SMS?

If it is plain text, it must be ordinary SMS, and if there are pictures, it must be MMS. There is also opening the theme and entering Settings-> [Information]-> Select [Show Subject Bar] in [SMS/MMS]. When sending a message, as long as you enter the subject, whether there is a picture or not, it is a multimedia message. If the subject has no words or pictures, it is still an ordinary short message.