This feature is going to be rolled out to everyone and likely available for you already. Whenever you want to send a media file on WhatsApp, you will be able to toggle a setting that will set it to be viewable only once.
Within a chat, it will appear hidden and there you will be able to see its status to know if it was viewed by others or not.
How to test:
- Open any WhatsApp conversation.
- Tap on the attachment button.
- Pick a media type.
- Pick a media file.
- Tap on the 1 icon in the edit text field.
- Send it to the chat.
- 📲 WhatsApp is a popular messenger app by Facebook.
- 📲 WhatsApp is also available in Beta and you can opt-in as a tester via Google Play.