The author should not have included any monetary figure in the article as doing so brings down the wrath of a thousand pedants with pocket calculators proving he overcharges and overvalues his work. So many people here seem to think they somehow "got him" on some straw-man price-point that clearly does not exist.
Meanwhile, the figure he calculated clearly exists to make the point that creating such an image costs more to him than clicking Save As... did to you and he wants to be appropriately compensated in dollars.
The fact the comments here seem to lack the professional empathy to jump from "How do you make money? Charge for your webapp!" To "How do you make money? Charge for your photos!" really shows how myopic the community can be. Not everyone builds a career around trying to make social network v35.0
tl;dr Pay photographers for their work, like you pay any other professional.
edit: And for a real cherry on top, the blog post itself appears to be taken in whole from http://www.flickr.com/photos/johnmueller/6643032477/in/photo... I suppose John Mueller could have agreed to have his content republished but nothing indicates that to be the case and a skimming of the petapixel blog doesn't seem to include many guest contributors.
The author's real blog is at http://johnbmuellerphotography.blogspot.com/