Fans of the Beatles are being invited on a web-based scavenger hunt for footage from the group's Let It Be recording sessions, as part of a promotional campaign for the release of The Beatles' Let It Be..Naked on iTunes. The 1970 album has not been available digitally before. Clues will be released this week on The Beatles' Facebook and Twitter feeds, leading fans to sites where they can unlock pieces of the puzzle. Sites so far include buzzfeed.com and Rolling Stone's online archive. Those who find all three pieces can unlock the full video, which includes the fourth piece, on a specially created website.