

Discovered by a reddit user this morning, the hidden trick works in any app that lets the iPhone's volume buttons be used to take a photograph. Examples include Snapchat, Camera+, and Manual, all apps where the iPhone's volume button works in the same way as a press on the on-screen photo capturing button.
To use the Apple Watch as a remote trigger, open a compatible app like Snapchat, open up the Music Glance, and turn the Digital Crown. The action will cause the camera to take a photograph, much like pressing on the iPhone's volume button would do. It also works within the Music app itself.
Though the Apple Watch can be used as a remote trigger for compatible apps through the Music Glance, the function is not as feature rich as Apple's remote control option for the built-in camera. With the default camera, the Apple Watch can turn the iPhone on and capture a photograph.
Article Link: Apple Watch Digital Crown Works as Remote Shutter for Camera Apps Using Music Glance