Just a GA pilot here, but the idea of sending a pic to the locked cockpit is a good one although I doubt that flight crew usually has much knowledge in identifying suspect devices. The upside is that two more gets a chance to say "Hey, isnīt that the whatever-thingy that is supposed to lie there?" but as long as both the CC and FC isnīt 100% sure of what they are looking at they should (in my mind as pax) sort that out on the ground. The potentially dangerous situation that might happen is that the mobile picture is sent to some sort of Ops Center per SOP and time is spent while locating someone there to try and id the thingy, while tick adds to tock...
Hope that makes sense, english isnīt my native language, lol.