haha, that's an old one. The guy on the picture actually made this modification himself in order to play a prank with his friends, it was never meant to go viral, but in the end, it did go viral.
Fact is, he was actually standing on the real WTC, the same that was rammed by planes on 9/11. However this picture was shot about 5 years (if I recall correctly) before that attack... The plane was for the prank photoshopped in, the rest of the picture is real.
