I love that comic— but
The joke relies on the fact that panel 1 is ultra clean, Panel 2 has some slight, barely visible artifacting, Panel 3 is a screenshot, and panel 4 has a watermark, and is cropped as well
But if you visit the xkcd website, that comic has been rescaled, so that the first panel is jagged, with antialiasing artifacts, and it no longer is qualitatively different from the second panel. Oh Irony!
