Frank P. Walentynowicz

Setting featured images for posts / pages could be very time 
consuming, especially when your media library holds hundreds of 
pictures. Very often we select the same thumbnail for posts in 
particular category. This plugin automates the process by inserting a 
thumbnail based on category / thumbnail mapping while post / page is 
being created or updated. Now bundled with FPW Post Thumbnails.

FPW Category Thumbnails

Assigns a thumbnail based on categoryid/thumbnail mapping to a post / page when the post is created or updated. Built-in FPW Post Thumbnails.

Risto Niinemets

junkcoder

AJAX Thumbnail Rebuild allows you to rebuild all thumbnails on your site. There are already some plugins available for this, but they have one thing in common: All thumbnails are rebuilt 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 rebuild your thumbnails.
Why would you want to rebuild 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 rebuild all thumbnails. But instead of telling the server to recreate all thumbnails at once, they are rebuilt one after another. Rebuilding 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 rebuild, so that you don’t need to recreate all images if you’ve just changed one thumbnail-size. You can also choose to only rebuild post thumbnails (featured images).
This plugin requires JavaScript to be enabled.
Contributions are welcome at <a href="https://github.com/breiti/ajax-thumbnail-rebuild" rel="nofollow ugc">Github</a>

AJAX Thumbnail Rebuild

AJAX Thumbnail Rebuild allows you to rebuild all thumbnails at once without script timeouts on your server.

FPW Category Thumbnails vs AJAX Thumbnail Rebuild