Holoportation is now a thing, so start slapping everyone in arm's distance to make sure they're real.
This new technology by Microsoft Research uses 3D motion capture and Microsoft's HoloLens mixed reality hardware to "holoport" people from one place to another, which is definitely going to contribute to a universal feeling of paranoia in the future. HOW DO I KNOW YOU RE REAL PERSON IN FRONT OF ME? The technology can be used live, but you can also create 3D recordings that can be scaled and played back at will -- meaning Star Wars-style holo-messages are inching closer to reality.
Cameras placed around the subject capture them from every angle, allowing this system to create rendered model, which is a grey blocky version that sort of looks like a character from ReBoot. It then gets textured to more closely resemble the actual human its supposed to be, before -- most impressively -- that data gets compressed and transmitted with reasonable fidelity to a new location. How it's possible to send that much data is beyond me, considering YouTube videos barely work on my shitty Comcast wifi.