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.

Muhammad Umer Shahzad

Smart Image Optimizer is a powerful and lightweight plugin that:
<ul>
<li>Compresses uploaded images to reduce file size.</li>
<li>Converts images into modern formats like JPEG, PNG, AVIF, WebP, and more.</li>
<li>Retains visual quality using lossless or smart lossy compression.</li>
<li>Enables lazy loading to improve page speed.</li>
<li>Automatically optimizes images during upload.</li>
<li>Allows bulk optimization of existing media.</li>
</ul>
This plugin is ideal for bloggers, photographers, eCommerce stores, and all WordPress users aiming to improve performance and user experience.
<h3>Features</h3>
<ul>
<li>✅ Lossless and lossy compression options</li>
<li>✅ Format conversion: PNG ↔ JPEG, AVIF, WebP</li>
<li>✅ Automatic optimization on upload</li>
<li>✅ Bulk optimization of media library</li>
<li>✅ Lazy load for all images</li>
<li>✅ No third-party API required (works locally)</li>
</ul>
<h3>License</h3>
Smart Image Optimizer is open-source software licensed under the <a href="https://www.gnu.org/licenses/gpl-2.0.html" rel="nofollow ugc">GPLv2 or later</a>.

Smart Image Optimizer

Smart Image Optimizer compresses image sizes and converts them to modern formats like JPEG, PNG, AVIF, and more — for faster websites and better SEO.

Disable WebP By Default vs Smart Image Optimizer