We already knew that the Tupac Hologram wasn't really a hologram but rather a modern regurgitation of the old mid-19th century trick known as "Pepper's Ghost". If you were confused on how that illusion worked, be confused no more! Here it is.
Roxanne Palmer at the International Business Times made this infographic that clearly illustrated how the whole hologram shenanigans worked. AV Concepts, the company behind the fauxlogram, used Musion Systems' Musion Eyeliner setup to project a 2D animated Tupac onto an invisible (to the audience) screen to make him look 3D. [IBTimes]