When a beloved actor or musician passes away, they always leave behind that lingering thought of what they might have been able to create if they'd only had a little more time. However, as John Lennon's posthumous chart success has shown, for the stars of the future, death doesn't need to be the final curtain call. From actors making ghostly returns to the screen or famous figures narrating the story of their own lives, AI is reviving more than just celebs' careers. But when stardom doesn't end with death, who gets the final say on a celebrity's legacy? Here, MailOnline reveals how these creepy technologies are bringing back your favourite figures from the past to perform again.