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.
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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.
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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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<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

Every time you upload an image, WordPress doesn’t just store your file — it generates a separate cropped copy for every registered image size. A fresh install already creates three (thumbnail, medium, and large) on top of the original, so a single upload becomes four files on your server.
Themes and plugins add many more. A typical site might register hero, slider, product thumbnail, team member, and testimonial sizes — and WooCommerce adds several of its own. With six registered sizes, one upload turns into seven files, even when the page only ever displays one of them. The rest sit on disk doing nothing but consuming space.
Multiply that across hundreds of posts, pages, and products and the waste adds up fast: bloated storage, slower backups, and longer upload processing. It’s especially painful on WooCommerce sites, where uploading a single banner or hero image also generates the full set of product thumbnail sizes you’ll never use for that image.
WP Image Sizes fixes this by letting you decide which sizes WordPress is allowed to create.
<ul>
<li>Per post type control — Assign the exact image sizes that matter to each post type from a simple settings page. A slider post type might only need one large size; testimonials might only need a thumbnail.</li>
<li>Choose sizes at upload time — When you add media, the uploader shows the available sizes so you can pick what gets generated for that specific upload.</li>
<li>Disable thumbnails entirely — Skip generating any additional sizes for a post type or a single upload when you only need the original.</li>
<li>No lock-in — WP Image Sizes never caches or alters your files. Any images already generated stay intact, even if you deactivate or remove the plugin.</li>
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The result is a leaner media library, less wasted disk space, and a faster, lighter WordPress site.
<h3>PRO</h3>
The free plugin controls which sizes get generated on new uploads. WP Image Sizes Pro extends this to your existing media and adds automation:
<ul>
<li>Bulk Create Image Sizes — Generate selected image sizes for all existing images of a chosen post type. Perfect after registering a new size or switching themes.</li>
<li>Bulk Delete Image Sizes — Remove unwanted image size files from existing media to reclaim server space in one click.</li>
<li>Create Images on Runtime — Automatically generate a missing image size the moment it is first requested on the front end, instead of pre-creating every size.</li>
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<a href="https://aiwatech.com/product/wp-image-sizes-pro/" rel="nofollow ugc">Get WP Image Sizes Pro</a>

WP Image Sizes

Take control of the image sizes WordPress generates. Pick only the sizes you actually use, per post type, and reclaim wasted server space.

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