Unraveling The JPEG
A deep, deep, deep dive into the JPEG format. Best of all, it’s got interactive explanations you can tinker with, a la Nicky Case or Bret Victor.
Retina revolution
You’ve probably seen this already, but it’s really worth bearing in mind: when you’re scaling up JPGs for retina display you can safely reduce the image quality by quite a lot—to the point of getting the exact same file size as a higher quality image that’s half the size.
Related links
google/guetzli: Perceptual JPEG encoder
Google have released this encoder for JPEGs which promises 20-30% smaller file sizes without any perceptible loss of quality.
JPEGmini - Your Photos on a Diet!
This looks like a really handy tool for reducing the file size of JPEGs without any perceptible loss of quality (in much the same way that ImageOptim works for PNGs)—available as a Mac app or an installable web service.