Shellbot

** 07/06/18 – Updated for the latest version of WooCommerce **
By default, WooCommerce displays a neutral and uninteresting category image placeholder in those cases where a category has 
no explicitly set thumbnail. This plugin simply replaces the placeholder image with a product image from that category.
User can choose whether to use a random product or the latest product from that category.
Feature requests welcome, please <a href="https://wordpress.org/support/plugin/woocommerce-auto-category-thumbnails" title="Plugin support forum" rel="ugc">post in the support forum</a>.
Usage
There is no complicated setup, simply install the plugin and configure WooCommerce to display categories. Any categories containing products but without a 
category thumbnail will now display a product image.
To switch between random and latest product display, see the settings page under WooCommerce > Settings > Auto Category Thumbnails.
More options coming soon. <a href="http://codebyshellbot.com/wordpress-plugins/woocommerce-auto-category-thumbnails/" title="WooCommerce Auto Category Thumbnails" rel="nofollow ugc">Plugin release page</a>.

WooCommerce Auto Category Thumbnails

Replace the default WooCommerce category image placeholder with a relevant project image instead.

olivecart

WP-OliveCart4 is a free e-commerce plugin made in Japan. 
With WP-OliveCart4, you can easily to e-commerce shop on WordPress.
WP-OliveCart4はWordPressにショッピングカート機能を追加する日本語対応、日本製プラグインです。 
今あるサイトをシンプル＆簡単にショッピングサイトに。

WooCommerce Auto Category Thumbnails vs WP-OliveCart