Description
If you want to resize featured images (post thumbnails) on the fly for your posts automatically then this plugin can help you.
To take effect just open a post or page and all featured images in that post will be resized to a normal size.
This plugin can be very useful after a theme install.
It can be an alternative for Regenerate Thumbnails plugin.
I think this plugin is better because you will not need to wait before all images are resized for all different sizes, just for images that are need to resize.
The plugin will keep the original copy of all image files.
Screenshots
Admin Panel of the plugin. 
After theme change, you can see that featured images looks weird 
After plugin activation, the resized featured images (the result)
Installation
- Upload the plugin folder to the
/wp-content/plugins/directory, or install the plugin through the WordPress plugins screen directly. - Activate the plugin through the ‘Plugins’ screen in WordPress
- To change the settings, go to Dashboard -> Plugins -> Resize Post Thumbnails
- That’s it!
FAQ
- Why should I use this plugin?
-
After you changed a theme that uses custom post thumbnails sizes that requires the images to be resized then this plugin can help out.
- Will it break any other plugins?
-
I don’t think so.
- Won’t this conflict with plugins?
-
Well I can’t tell for sure.
- Can you add a feature X?
-
Depends, if its useful enough and I have time for it.
Reviews
Contributors & Developers
“Resize Post Thumbnails” is open source software. The following people have contributed to this plugin.
Contributors
Translate “Resize Post Thumbnails” into your language.
Interested in development?
Browse the code, check out the SVN repository, or subscribe to the development log by RSS.
Changelog
1.2
- Add support for size in array format like: array( 500, 250 )
1.1
- Remove srcset attribute from featured images
1.0
- First release.