When you receive a disappearing photo or video, a little photo button appears at the top of your inbox to indicate which account sent it to you. When you tap it, it will begin playing immediately and play/stay on your screen for eighteen seconds. After that, it is gone. You have the option to reply to the photo/video in kind i.e. with a disappearing photo or video of your own. When you get a disappearing photo or video from someone, their profile picture will appear at the top of your inbox with a colorful ring around it.
You can tap someone's profile picture to view messages they've sent and reply to them. Disappearing photos and videos are a conversation of their own. They will not appear in a direct message thread in your inbox. You will be able to tell when your photo/video has to be viewed by your recipient. You can only send and receive these disappearing messages from an account that you follow and that follows you back. This should effectively prevent spam.