Al Findlay has a strange website called "That Was Me" with the strange purpose of identifying background lurkers that accidentally (or not) got into the photo.
This one is taken by EdT, who commented:
"Less of `That was me!`, and more of `That was my father!`; my Dad got so pissed off with being asked to get out of the way of people`s photos that he started standing behind groups of tourists with an inane smile on his face. I happened to be standing behind the photographer and caught him in the act. So, if you`re a member of that Argentinian school group and you`re wondering who the hell the strange guy is in the top- right-hand corner, now you know... I`m so dreadfully sorry"
http://www.thatwasme.net/showphoto.php?photoid=10 - Thanks Al!