Out of curiosity, why can't we just replace the actual files ourselves?

The background for WPTavern is https://wptavern.com/wp-content/uploads/2013/12/wood13.jpg

Jeff can upload http://marketingland.com/wp-content/ml-loads/2013/03/Matt-Mullenweg.jpg (a photo of Matt Mullenweg), before uploading it he changes the file name to wood13.jpg then uploads it. Anyone that sees the site 1 second after the upload will see matt mullengweg's face istead of the woodie background.