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.

dmikam

This simple plugin permits you to upload images to categories, tags and custom taxonomies just like to posts. 
This feature is very useful when you want to show unique image in header tor every category or even some slideshow of images. 
Also you can show a list of categories/subcategories with a little thumbnail am much more.
By the way, this plugin just uses wordpress native functionality – no aditional tables and nothing like that. 
Also it uses wordpress images so all sizes are generated automatically (custom sizes included).

WP Category Images

Simple plugin that permits to images to Categories, Tags and Custom Taxonomies.

SimpleRecentThumbs vs WP Category Images