How to Create a Hologram Onstage
The stage illusion “Pepper’s Ghost” is about 150 years old:
https://en.wikipedia.org/wiki/Pepper%27s_ghost
Here’s a modern high-tech version, which uses a mylar screen instead of glass. Musion’s “Eyeliner” system was the one used to bring Tupac back from the dead at Coachella, and to let Madonna sing with the Gorillaz: