For this edition of Flickr Friday, we have a composite photo: GMs Ponomariov, Korchnoi, Kasparov, Spassky, and Karpov. All were World Champions (Ponomariov via FIDE KO in 2002) or World Champion caliber (Korchnoi, who came within one game of winning the title in 1978).
The description added, 'Chess simultaneous exhibition in Zürich Main Station (2009).' For more about the event, see Zurich: A chance to meet the World Champions on Chessbase.com:-
They will all be there, for the 200th jubilee of the oldest chess club in the world: the Schachgesellschaft Zürich. The festivities, which include a Jubilee Open, will see Anand, Karpov, Korchnoi, Kramnik, Spassky, Ponomariov and Topalov playing a Champions Rapid. They are joined by Garry Kasparov for a Champions Simul against 200 opponents.
The event was also covered in the book The Zurich Chess Club, 1809-2009 by Richard Forster, which I mentioned in a recent post on McFarland Chess Books.