A dude (who looks a little bit like the TMZ guy but is actually comedian Greg Benson) went to Hollywood to prank the balls out of some unsuspecting tourists. Never trust a man who willingly offers to take a photo of you, because he's going to magic himself into the background of that photo and film you freaking out.
Benson uses a cardboard cutout of himself to take the "magic" photos, because apparently people looking at a camera are not capable of distinguishing between a 2D mock-up and and 3D jokester.
The most tragic moment comes around the 40 second mark, when Benson asks a couple if they want another photo of them, this time without him in the background. They oblige, and then he shows up in that one, too.
See, Internet pranks don't always need to be mean-spirited and ruthlessly deceptive. They can also be fun and moderately deceptive.