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.
</li>
<li>
Go into Child Categories makes the plugin look in child categories too, useful if you have products buried in quite a deep category structure.
</li>
<li>
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>
<li>
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.
</li>
<li>
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.
</li>
<li>
Custom Transient Expiry can be used to define your own transient expiry period (in seconds) if none of the pre-defined options are suitable.
</li>
<li>
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.
</li>
</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.

aiwatech

In modern web designs, designers create different sizes of images on the web pages for attractive layout. If a web page is built using wordpress, a developer has to register every image size in theme to make sure, if client uploads an image of different size, it does not break the layout.
With a new WordPress installation, by default it creates three sizes e.g. thumbnail (150 x 150), medium (300×300), large (1024×1024) which means whenever a new image will be uploaded, WordPress will keep at least four copies of images on the server, one original image and 3 cropped image copies based on image sizes.
When developer/designer needs different size of image, they will register more image sizes e.g. hero, product thumbnail, product large image, team member image etc depending on design of the page.
Now lets say we have 3 default and 3 custom image sizes defined in theme, and now whenever a new image will be uploaded, WordPress will create 6 image copies and 1 original image even we need to use only 1 for a specific area on the website, remaining copies will remain on the server and will occupy space. Imagine when we have lots of posts, pages having different images, how many unnecessary images WordPress creates on the server which are useless and just eat server space. In case of Woo-Commerce website if you need to upload a new slider image for home page or a hero image for about page, it will create a lots of copies including different sizes of products image sizes which woo-commerce registers itself.
Ultimately website speed gets effected and server space as well.
To solve this issue, we built a plugin WP Image Sizes this plugin allows user to decide which image sizes should be created for every image being uploaded through WordPress.
After installing WP Image Sizes, it will create a setting page from where user can assign image sizes to each CPT. e.g. user can assign one size for hero/slider CPT, one size for team member, testimonials. After assigning image sizes to each CPT when user will upload a new image, WP Image Sizes will only allow WordPress to create copies of image sizes which were assigned to the CPT.
In case user tries to upload an image from a Media, it will show options in media uploader to select which image size user wants and WP Image Sizes will only create that image size.
WP Image Sizes plugin saves a lot of space on the server and plays a role to make WordPress website a bit fast.
<h3>PRO</h3>
WP Image Sizes plugin is also available in a professional version which includes more features <a href="https://aiwatech.com/product/wp-image-sizes-pro/" rel="nofollow ugc">See here</a>

WP Image Sizes

Select the only image sizes for post types you want to be generated. Eliminate unnecessary image sizes.

GazChap's WooCommerce Auto Category Product Thumbnails vs WP Image Sizes