Kate Moss at Alexander Mc Queen Fall 06/07.
From The Independant(Susannah Frankel):
Moss in person was, in fact, nowhere to be seen. Rather than stalking the bare floorboards alongside her contemporaries, she had been filmed prior to the show and away from the crowds and her image was projected via an optical device, widely known as Pepper's Ghost, an effect first employed by the mid-19th century chemist John Henry Pepper for a production of Charles Dickens' The Haunted Man.
Some info on Pepper's Ghost: