The "resurrection" of rapper Tupac Shakur wowed audiences at the Coachella music festival. But the illusion isn't a hologram, as some have reported -- it's actually a 2-dimensional video cleverly projected using technology based on an old theatre trick. 

Tempe, Ariz.-based AV Concepts orchestrated Tupac's performance using Musion Systems Ltd.'s Musion Eyeliner setup that was able to project an animated version of Tupac (created by visual production house Digital Domain) onto a screen that appeared invisible to the audience.

By Roxanne Palmer

The Musion eyeliner system is based on "Pepper's ghost," a theater technique for producing illusions that has been used for centuries in plays and magic tricks.

In the stage version of the illusion, an actor is hidden in a recess below the stage and faces a mirror. The audience sees the actor's ghostly image reflected in a sheet of glass suspended above the stage, and lighting can be used to make him "appear" or "disappear."