We have all been using Jpeg now since the web started, however there are some modern alternatives appearing and Jpeg is starting to look like something that will soon be sidelined as a legacy format for browsers. There have been other alternatives that never gained traction, however Webp is a Google initiative and Apple are pushing HEIF, however that is for storage purposes at present.
Webp offers very good quality with typically smaller sizes than jpeg. Initially it only worked with Chrome, however that has now extended to cover most browsers, including Firefox, Opera and Edge. The notable exception is Safari, however they are apparently in development. https://caniuse.com/#feat=webp
I had a quick play in Blocs, but the format does not appear to be recognised at present. There is a free app that allows you to convert Jpeg to Webp and I saw a Jpeg saved for web drop from 128kb to just 81kb when converted to Webp. Multiplied across image heavy websites that would be a major saving.
There is an image stack for Rapidweaver that serves either Jpeg or Webp dependent on the user’s browser and that seems like a good solution. Webp is the default option with Jpeg served for legacy browsers. Jpeg support will undoubtedly be needed for quite a few years.
At the moment Webp files cannot be easily previewed in the finder here on Mojave, but they are visible when opened in Chrome or Firefox. Any thoughts from others on the future direction we should be aiming at?