Forget JavaScript, It’s Time for Browsers to Speed Up Images

The average webpage is now 1.2 megabytes and around 60 percent of that rather large payload comes from images. That’s a lot of data, whether you’re handling images responsively or just trying to speed up a desktop site.

And in fact there’s already a way to solve this problem with HTTP headers, namely the Accepts header, which tells the server which image formats the browser supports. Based on that information the server could then “re-encode, recompress, resize, strip unnecessary metadata and deliver the optimal format.”