marynixie

This plugin generates Featured Image for all posts at once.
It is based on WordPres 2.9+ feature – Post Thumbnails. This plugin takes the first image (by default) from post body and assignes it as a post Featured Image. It helps if your theme supports post thumbnails feature and you want to assign Featured Image for all your existing posts.
Plugin performs mass manipulation on posts Featured Image property and uploads files if they are stored externally. Don’t forget to backup your files and database before using this plugin.
It displays log of success/fails. There is also a feature to remove all Featured Images from all posts – this only changes post setting, no actual files are removed.
Related Links:
<ul>
<li><a href="http://wordpress.shaldybina.com/plugins/generate-post-thumbnails/" title="Generate Post Thumbnails Plugin for WordPress" rel="nofollow ugc">Plugin Homepage</a></li>
</ul>

Generate Post Thumbnails

Tool for mass generation of Wordpress posts thumbnails using the post images.

nosilver4u

Pedro Elsner

Force Regenerate Thumbnails allows you to delete all old images sizes and REALLY regenerate the thumbnails for your uploads.
Regenerate all thumbnails from the Tools admin menu. Regenerate batches of images via the Media Library list mode. Select the images to regenerate and then use the Bulk Actions drop-down menu to Force Regenerate Thumbnails. Use attachment actions to regenerate thumbnails for a single image.
Several filters exist for advanced usage. See more via <a href="https://gist.github.com/nosilver4u/eb858df10521aece2044a3a15ccdd17b" rel="nofollow ugc">this gist</a>.
You may report security issues through our Patchstack Vulnerability Disclosure Program. The Patchstack team helps validate, triage and handle any security vulnerabilities. <a href="https://patchstack.com/database/vdp/force-regenerate-thumbnails" rel="nofollow ugc">Report a security vulnerability.</a>

Force Regenerate Thumbnails

Delete and REALLY force thumbnail regeneration.

Generate Post Thumbnails vs Force Regenerate Thumbnails