gazchap

By default, WooCommerce will only show thumbnails for categories if the category has a thumbnail set.
This plugin changes this behaviour so that WooCommerce will hunt for a product thumbnail in the category being displayed, and use that instead.
Upon activation, the plugin will configure itself with the basic settings. Any categories that you have on your WooCommerce store that do not have a thumbnail set will then start displaying any available product thumbnails inside the category.
There are a number of options, these can be found in WooCommerce -> Settings -> Products -> Auto Category Thumbnails.
<ul>
<li>
Thumbnail Size sets the image size that the plugin should use when displaying the thumbnails. Defaults to shop_thumbail, but shop_catalog may be a better option for some themes.
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Go into Child Categories makes the plugin look in child categories too, useful if you have products buried in quite a deep category structure.
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Random Thumbnail tells the plugin to pick a random product thumbnail from those it finds every time the page loads – otherwise it always uses the first one it finds.
</li>
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Use Transients tells the plugin to save the thumbnail it picks for a category as a transient in WordPress, so that it won’t have to do it again while the transient is still active. This can hugely increase performance on sites with many categories, so is enabled by default.
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Transient Expiry is the length of time each transient is active for before the site picks another thumbnail for the category. By default it is set to 1 day.
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Custom Transient Expiry can be used to define your own transient expiry period (in seconds) if none of the pre-defined options are suitable.
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Exclude Thumbnail IDs accepts a comma-separated list of attachment IDs from the WordPress Media Library. The plugin will never use any thumbnail with one of these IDs for a category.
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</ul>
<h3>License</h3>
Licensed under the <a href="http://www.gnu.org/licenses/gpl-2.0.html" rel="nofollow ugc">GNU General Public License v2.0</a>

GazChap's WooCommerce Auto Category Product Thumbnails

Pick WooCommerce category thumbnails automatically from products contained within those categories.

brokenlibrarian

SimpleJPEGQuality is a plugin that adds a JPEG quality setting to the WordPress media settings page, which is used to determine the image quality of thumbnails, post images, headers, and other images which have been uploaded and then resized by WordPress. It will have no effect on the quality of the original uploaded images, or that of any images that were resized before this plugin was installed.
This plugin will also affect the quality level of JPEGs resized by plugins that use the image functions of WordPress (such as Auto Post Thumbnail). Image plugins that use their own code (such as Lazyest Gallery, Ungallery, and Post Thumbnail Editor) will not be affected.
The plugin 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.

SimpleJPEGQuality

SimpleJPEGQuality is a plugin that adds a JPEG quality setting to the WordPress media settings page, which is used to determine the image quality of t …

GazChap's WooCommerce Auto Category Product Thumbnails vs SimpleJPEGQuality