Sutolix

Informatiza

Automatically convert all images (png and jpg) sent to the WordPress library to webp.
ATTENTION: The original images are not kept, when sending an image it will be as if you had sent a webp from the beginning.
Features include:
<ul>
<li>Set conversion quality.</li>
<li>Set the maximum width/height of images. If an image exceeds the defined value in height or width, the image will be resized to the defined maximum.</li>
<li>Ignore images that have a certain name in the file name</li>
</ul>

Webp Transformer

Convert images from library to webp and resize them during upload

mores

This plugin is basically just a little improvement of <a href="https://wordpress.org/extend/plugins/resize-at-upload/" title="Resize-At-Upload" rel="ugc">Resize-At-Upload</a>, a fabulous plugin by A. Huizinga.
The plugin will automatically resize an image upon upload, depending on the maximum width and height that you define. Gone are the days when you, or your client, will ruin a site’s layout by uploading a huge file with 25 megapixels. 
Be advised: there is no backup, no copy of the originally uploaded image.
The plugin uses a class originally from Jacob Wyke (www.redvodkajelly.com).

Resize at Upload Plus

Automatically resize (i.e. scale down) images after uploading. Save disk space and preserve your layout

Webp Transformer vs Resize at Upload Plus