WebP is a next generation image format spearheaded by Google since 2013, which provides advanced compression options. While it is so much better than legacy formats, it is only supported at the moment of writing (February 2018) by Chrome, and Opera on desktops and Android (see Can I use WebP image format? for more details). As of today, Firefox is not scheduled to support WebP in future versions.
For an overview of WebP format and its shocking compression ration, see WebP: Another Google Project Behind the Scenes.
Practical solution is to serve images conditionally depending on the client browser WebP support. This recipe discusses how to do it with nginx.
There is even better coming soon: AVIF Revolution!
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