David Baumwald

*** 2022-09-12 UPDATE *** 
@matt published a post and codified a final decision that <a href="https://make.wordpress.org/core/2022/09/11/webp-in-core-for-6-1/" rel="nofollow ugc">WebP by default would not be coming to WordPress Core in version 6.1</a>. That being the case, this plugin will not be necessary for users to prevent WebP generation by default as part of the Core upload process.
Proposed to be included in WordPress 6.0 is a new feature to generate and use webp images by default. Specifically, when an image is uploaded, a WebP version of every image subsize is created. According to <a href="https://make.wordpress.org/core/2022/03/28/enabling-webp-by-default/" rel="nofollow ugc">the proposal</a>, one downside is that generating WebP versions along with the original JPEGs will “use an additional ~70% of the storage space to store both file types.” Although this is hugely beneficial to most websites and, more importantly, their visitors, some site owners may not be immediately able to increase the size of their storage to accommodate the additional files. For more information, see the proposal or <a href="https://core.trac.wordpress.org/ticket/55443" rel="nofollow ugc">the Trac ticket</a>.
To help site owners manage the transition, this plugin adds a setting under Settings -> Media to either enable or disable WebP creation on the initial upload of JPEGs. For Multisite installations, the plugin can be activated network-wide or on individual sites.
*** 2022-07-22 UPDATE *** 
Although the original implementation was not merged in 6.0 due to community feedback, changeset 53751(https://core.trac.wordpress.org/changeset/53751) merged an updated implementation that addresses some(but not all) concerns from the community. This merge will be part of the 6.1 release, unless further changes are needed. Some site owners may not be able to immediately cope with doubling their required storage allotment with their host, so the original goal of this plugin remains. The code has been updated to disable WebP creation on upload globally. There is a new ticket discussing the possibility of making this feature into a setting(see https://core.trac.wordpress.org/ticket/56263). However, given WordPress’s core philosphy of “Decisions, Not Options”, it’s unlikely to proceed.

Disable WebP By Default

Thank you for creating this plugin!  It's a shame it's necessary, but I appreciate that you created it to make it easier for site owners to be able to take back control over their sites without needing to know how to add a filter.

Thank you!

Thank you for your work with this plugin (and just keeping track and reporting all the latest WEBP changes, etc.). Great to find so much useful information in the plugin documentation. Very much appreciated!

Thank you

A small plugin to control WebP image creation when JPEG images are uploaded.

robertcpalmer

Supercharge your site with instant-loading images (WebP)
Give your website a speed boost in minutes. This plugin converts and compresses your images to the modern, ultra-efficient WebP format—so pages feel snappier and visitors stick around longer.
Why you’ll love it!
Faster pages, happier users: WebP files are smaller, so images load noticeably quicker, but the quality stays sharp. Even when using a Compression Setting of just ‘1’.
Set & forget: Convert and compress everything in your Media Library, then let the plugin automatically optimise new uploads.
No workflow change: In the WordPress admin, you’ll still see images in their original formats. On the front end, however, visitors get the magic: lightweight, crystal-clear WebP files.
Totally FREE! There are no PRO versions to sell or the pushing of unnecessary CDN services, data-limited APIs or any Registration. Use without limits.
Safe rollback: Want to switch back? DEACTIVATE the plugin to serve your original JPG/JPEG/PNG files again — WebP copies are removed as part of the process.
<h4>How it works</h4>
Convert existing images in your Media Library to WebP.
Keep the automatic conversion on for all future uploads.
Enjoy noticeably faster page loads without touching your content.
Pro tips (read me!)
-After converting, flush all caches: any caching plugin (e.g. WP Rocket), server-side cache, and your browser cache (Windows: Ctrl+Shift+R; Mac: ⌘+Shift+R).
-If you deactivate the plugin to revert to originals, flush caches again to ensure changes show everywhere.
-If you upload an image in WebP format, because it will have no fallback jpeg/png file, if you deactivate the plugin, that image will NOT be lost when all WebP files are deleted.
-Important: ALWAYS back up your site before activating or deactivating this plugin.
** Ready to make your images smaller, sharper, and faster? Install now and feel the difference. 🚀
<h3>FAQs</h3>
= If I deactivate the plugin and then reactivate it again, will I need to convert all my images again? = 
Yes. On deactivation of the plugin, it performs a full rollback, and all WebP images created by the plugin will be deleted, and your original files jpg/png will be served. Where you have WebP files that do not have a fallback file, those files will not be removed.
<h4>What Compression Level should I set?</h4>
If your existing images are of reasonable quality, set the Compression Level to ‘1’ and get image compressions of an amazing 90%+ and get excellent performance enhancements on your site, and the quality and sharpness of the images will also amaze.

Images to WebP Converter

Convert and Compress your Image Files into WebP Format. With compression rates up to 90+%.  Make your images and pages load instantly.

Disable WebP By Default vs Images to WebP Converter