Please be aware that PropDog does not recommend this effect! There is a lot more that has to go on to acheive this effect than is shown on the trailer, with a lot of audience management required.
Photo is a mere reflection of reality.
Imagine your spectator signs a blank card.
With your spectator's phone, a photo of spectator holding their own signed blank card is taken.
The spectator thinks of a playing card.
Their own signed blank card turns into a SIGNED thought of card in their OWN phone.
This is crazy!
Alter the digital reality.