Nico

<a href="http://nextgenthemes.com/plugins/regenerate-thumbnails-reminder/" rel="nofollow ugc">Plugin Page</a>
A small reminder in your admin area every time a image setting was changed (in media options, through a theme or plugin)
You most likely want to regenerate the thumbnails after this plugin reminds you to do so, if not already done I suggest you install the most used plugin Regenerate Thumbnails for this. This plugin will offer a redirection to <a href="https://wordpress.org/plugins/regenerate-thumbnails/" rel="ugc">Regenerate Thumbnails</a> in the admins reminder notice, but you can use any other plugin/method you prefer to regenerate thumbnails, just click dismiss when the reminder shows up and then manually navigate to your preferred regenerate plugin.

Regenerate Thumbnails Reminder

Checks if your image sizes have changed or if there was a new one added, if so it reminds you to go regenerate them.

codersantosh

Acme Themes

Regenerate Thumbnails – Acme Fix Images is a handy WordPress plugin designed to resolve issues related to image thumbnail sizes. If you’ve recently adjusted image sizes in your Media Settings or encountered display problems due to improper thumbnail sizes, this plugin can help you ensure consistency and proper display of images across your website.
<ol>
<li>Log in to your WordPress admin panel.</li>
<li>Navigate to Appearance => Acme Fix Images.</li>
<li>Select the image sizes and options you wish to fix.</li>
<li>Click “Fix All Images” to regenerate thumbnails according to your chosen sizes.</li>
</ol>

Acme Fix Images – Regenerate Thumbnails

Fix image sizes after you have changed image sizes from Media Settings. Ensure your images display consistently across your website.

Regenerate Thumbnails Reminder vs Acme Fix Images – Regenerate Thumbnails