The Lock-view feature allows an Aura to remain running if the user looses sight of the trigger image after the experience has activated.
You can add this feature in the Aura creation/edit page - it is a button at the left end of the overlay placement tools (which run along the bottom of the 2D work space).
Clicking the button adds a transparent lock-view overlay to your Aura - you can position it just like any regular overlay.
When the users device loses sight of the trigger image the Aura will effectively full-screen the lock-view overlay - along with anything inside its bounds. The whole Aura will remain active & if the user aims the device back to the trigger the Aura we re-attach itself and continue live-tracking to it!
Once added to an Aura, the lock-view area will display as an Overlay on the 2D canvas, it will be listed in the Overlay list at the top.
So that it doesn't interfere with the Aura creation, the lock-view area is "behind" the other Overlays in your Aura (in terms of clicking on it). So if you already have a bunch of overlays in place, simply hide them using their eyeball icon in the Overlays list until you can get to the lock-view Overlay.