mbecher

If your theme supports the thumbnail feature introduced in WordPress 2.9, this plugin will display attached thumbnails on the admin area’s manage posts and manage pages screen, similar to the media management page.

Admin Thumbnails

If your theme supports Wordpress 2.9's thumbnail feature, this plugin displays thumbnails on the admin area's manage posts and manage pages  …

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.

Admin Thumbnails vs Force Regenerate Thumbnails