The top picture appeared on the front page of the St. Louis Post-Dispatch. It showed amateur photographer Ron Olshwanger celebrating in the office of the paper's managing editor after being awarded the Pulitzer Prize for spot-news photography. The prize had been awarded to him for a picture (the one visible in the foreground) which he had taken the previous year showing a firefighter trying to save a 2-year-old girl. His wife, Sally, could be seen behind him. What couldn't be seen was the can of Diet Coke that had originally sat prominently on the table in front of him.
The bottom image is the original version of the photograph, with the can. The significance of the can was that Olshwanger was a teetotaler, so he wasn't celebrating his award with champagne. But an editor at the Post-Dispatch thought the can ruined the composition of the photo, so he ordered its removal. Apparently he meant for the photo editors to remove it by cropping it out (an accepted journalistic practice). Instead, they made it vanish by using a Scitex Machine to digitally delete it.
Links and References
Wheeler, T. (2002). Phototruth or Photofiction? Ethics and Media Imagery in the Digital Age. Lawrence Erlbaum Associates: pgs. 114-115.