After releasing the feature on Android last month, Facebook is debuting WhatsApp self-erasing media and texts on iOS via a new beta release, according to WhatsApp info site WABetaInfo. If you sign up for the beta version 22.214.171.124 on Testflight, you'll be able to send photos and videos that self-destruct as soon as they're viewed and dismissed. Users with access to the "view once" feature will see a dedicated button resembling a timer in the caption input field, as shown in the WABetaInfo screen capture below.
Unlike WhatsApp's disappearing messages, which delete after seven days, photos and videos sent using view once mode will vanish immediately after you close them. The sender will be notified when their media has been viewed.
As WABetaInfo notes, there's nothing stopping users from taking screenshots of media and you won't be notified if a recipient has done so. As a recipient, you can't block the sender from being notified after opening the message, either.