Theme Egg

Generate Thumbnail allows you to generate all thumbnails on your site. There are already some plugins available for this, but they have one thing in common: All thumbnails are regenerate in a single step. This works fine when you don’t have that many photos on your site. When you have a lot of full-size photos, the script on the server side takes a long time to run. Unfortunately the time a script is allowed to run is limited, which sets an upper limit to the number of thumbnails you can regenerate. This number depends on the server configuration and the computing power your server has available. When you get over this limit, you won’t be able to generate your thumbnails.
Why would you want to generate your thumbnails? WordPress allows you to change the size of thumbnails. This way, you can make the size of thumbnails fit the design of your website. When you change the size to fit for a new theme, all future photos you are going to upload will have this new size. Your old thumbnails won’t be resized. That’s where this plugin comes into action. After changing the image sizes, you can generate all thumbnails. But instead of telling the server to recreate all thumbnails at once, they are generate one after another. Generateing thumbnails for one photo won’t take all too long, so you won’t run into any script timeouts. Note that you still have to wait until all thumbnails have been rebuilt. If you close the page before the task is completed, you have to start all over again.
You can also select the thumbnail sizes you want to generate, so that you don’t need to recreate all images if you’ve just changed one thumbnail-size. You can also choose to only generate post thumbnails (featured images).
This plugin requires JavaScript to be enabled.

Generate Thumbnail

Generate Thumbnail allows you to generate all thumbnails at once without script timeouts on your server.

Subrata Sarkar

Custom Thumbnail Generator is a powerful tool for defining and managing custom image sizes in WordPress.
Key Features
<pre><code>* **AJAX-powered Interface:** Add, remove, and regenerate thumbnails instantly without a page reload. 

* **Theme Independence:** Custom image sizes are decoupled from themes, ensuring they remain accessible and functional even when themes are switched. 

* **Consistent Image Handling:** Provides developers, photographers, and content creators with precise control over image dimensions.
</code></pre>
<h3>License</h3>
This plugin is licensed under the <a href="https://www.gnu.org/licenses/gpl-2.0.html" rel="nofollow ugc">GNU General Public License v2 or later (GPLv2+)</a>.
You are free to use, modify, and distribute this plugin under the terms of the GPL license.

Custom Thumbnail Generator

Custom Thumbnail Generator manages image sizes via an AJAX interface. It decouples sizes from themes, ensuring they persist and remain functional.

Generate Thumbnail vs Custom Thumbnail Generator