A bit more info - the tech behind this is a 2d variation on the Pepper's Ghost illusion (
http://en.wikipedia.org/wiki/Pepper%27s_ghost ), apparently licensed from Musion (
http://www.musion.co.uk/). It's had previous outings - animators at Square Zero have used it several times, including to recreate Frank Sinatra.
http://www.squarezero.co.uk/what-we-do/hologramsIt's interesting to see their videos from 2010, which are still quite realistic but look stilted compared to the Tupac projection.
And obviously these aren't really holograms. I'm not connected to this in any way, just looked it up earlier since none of the articles mentioned what was driving this.