Aug 3 (Reuters) - Users of Facebook Inc"s (FB.O) WhatsApp can now send disappearing photos and videos on its platform starting this week, as it looks to better compete with Snap Inc"s (SNAP.N) photo messaging app Snapchat. The feature, called View Once, will let photos and videos disappear from the chat after they have been seen, Facebook said in a blog post on Tuesday, adding that once the media content has been viewed, the message will be shown as "opened." Snapchat, known for its Stories feature that lets users post updates that disappear after 24 hours, has grown in popularity last year as pandemic-induced curbs kept users at home. The company has also been adding new features on its messaging app to attract more users.