Nick Leghorn

This plugin adds a section to your Settings menu in the wp-admin section. Through that section you can perform two tasks:
<ul>
<li>A scripted, one-time action updating all of the posts in your blog that do not have a featured image where the script will either try to find a suitable image to use or use one you have provided and configure it for you.</li>
<li>An ongoing, continuous monitoring for posts that do not have a featured image, using the same logic to try and find a suitable featured image and setting that for the post.</li>
</ul>
You can find additional documentation for this plugin on the author’s blog <a href="https://blog.nickleghorn.com/2021/01/25/adding-a-featured-image-to-all-posts-in-wordpress-in-one-easy-click/" title="blog.nickleghorn.com" rel="nofollow ugc">blog.nickleghorn.com</a>
Special thanks to Robert Farago for giving me yet another massive site without any Featured Images to clean up for the impetus to finally make this available.

Featured Image Bulk Set Plugin

This is a plugin designed to do one simple job: programatically add a featured image in WordPress to existing posts. Either images already in the post …

Doug Wollison

This plugin is no longer being developed.

QuickStart

This plugin is no longer being developed.

Featured Image Bulk Set Plugin vs QuickStart