WordPress BPG Shortcode
BPG (Better Portable Graphics) is an image file format aimed at replacing JPEG and that implements a lot of desirable features from PNG (like translucency) and GIF (like animation). It's based on technology used in the HEVC video standard so it's kind of doubtful that we'll ever see it get widespread use due to patent concerns.
More about BPG
While my own website no longer runs on WordPress, I had put together a quick plugin for BPG compatibility a few years ago. If you think you might want to use the format on your own site, you can download it and give it a spin.
BPG Shortcode Plugin (ZIP)
I've added the polyfill to this site so that you can see some of the BPG files I generated in action.
A high quality photo that clocks in at 77KB.
A high quality animation in 48KB. (The original GIF was 1.9MB.)
32-bit translucency in 11KB.
Again, it looks like BPG is probably going to be a dead format soon. There's really no point in extending or maintaining the WordPress plugin at this point so there will be no further development. This page exists for people to download the old plugin in case they want to play around with it.