Omar Shehata: Unraveling the JPEG

“JPEG images are everywhere in our digital lives, but behind the veil of familiarity lie algorithms that remove details that are imperceptible to the human eye. This produces the highest visual quality with the smallest file size—but what does that look like? Let's see what our eyes can't see!”

This is a pretty amazing post going over what it takes to encode (and thus decode) a JPEG image. The best part is you can view the data of the sample images as numbers in a big text box, which you can change. And then the JPEG updates in realtime to show your changes.