The mask icon next to a guest's name indicates that the guest accessed your gallery using Private/Incognito mode in their browser.
When a browser is in Private or Incognito mode, it doesn't retain information, including details about a guest accessing your event's gallery. If they close their browser tab, GuestCam won't be able to remember them, which may result in them needing to re-enter their name with each visit, and creating duplicate guests.