brokenlibrarian

SimpleRecentThumbs is a widget plugin that shows a list of thumbnails from recent posts with featured images, optionally filtered by a category. Other than setting up the widget details, no configuration is required.
The thumbnails are in a widget-standard unordered list. The widget CSS class is widget_recent_thumbs and the thumbnail links are class post_thumb.
Leaving the category field empty will have the widget use thumbnails from all posts; posts without featured images will not be listed. Without a category specified, the “more” button option will do nothing.
Thumbnail size is as specified in the Media settings for WordPress.
SimpleRecentThumbs has no extra requirements and has been tested with the twentyten through twentyfourteen themes.
Development on this plugin has halted. Other developers should feel free to use the Apache-licensed code for their own projects.
http://brokenlibrarian.org/tinyplugins/ 
brokenlibrarian@gmail.com 
09/28/14
<h3>License</h3>
Copyright 2014 Christian Wagner
Licensed under the Apache License, Version 2.0 (the “License”); 
 you may not use this file except in compliance with the License. 
 You may obtain a copy of the License at
<pre><code> http://www.apache.org/licenses/LICENSE-2.0
</code></pre>
Unless required by applicable law or agreed to in writing, software 
 distributed under the License is distributed on an “AS IS” BASIS, 
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
 See the License for the specific language governing permissions and 
 limitations under the License.

SimpleRecentThumbs

SimpleRecentThumbs is a widget plugin that shows a list of thumbnails from recent posts with featured images, optionally filtered by a category.

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.

SimpleRecentThumbs vs Regenerate Thumbnails Reminder