tuxlog

The wp-webp Plugin gives your site the ability to show images in WebP format using WebPJS by Dominik Homberger 
It simply adds the javascript as describe at http://webpjs.appspot.com/ to your site. 
You can choose between adding to the header or the footer and you can choose if it’s added allways or just 
when the browser used does not support WebP itself.
Credits: 
 Thanks to Dominik Homberger who developed the grep WebPJS (http://webpjs.appspot.com/) 
 which is included in the subdir webpjs

wp-webp Plugin

The wp-webp Plugin gives your site the ability to show images in WebP format using…

Louis

This WordPress Plugin for WebP image uploads enabled WebP image uploads into the media library.
It will also add a class to the body tag for CSS selectors. This is helpful for setting background images.
Example:
selector {
background: url(‘images/example.jpg’); 
}
body.supports-webp #selector { 
 background: url(‘images/example.webp’); 
}
Use the function webpSupported() in template files to conditionally show WebP images.
Example: 
if (webpSupported()) : 
 WebP image here 
 else: 
 Image with other fallback format here 
 endif;
Major features in WP Enable WebP include:
<ul>
<li>Enabling WebP Image uploads into the media library. </li>
<li>Browser detection that adds a class to the body tag indicating WebP is supported by the browser.</li>
<li>Helper function to use in theme template files to check if the browser supports WebP image format.</li>
</ul>

WP Enable WebP

Works fine for uploading webp images. I set one up as a featured image, it loads fine on a desktop, but for mobile users also loads a full-size image. Does not scale it down like jpeg formats...

Would be great if the developer could continue his work on it.

Featured image in webp format does not scale down for mobile use

License: GPLv2 or later WordPress plugin to enable WebP image uploads.

wp-webp Plugin vs WP Enable WebP