WooCommerce shows a placeholder when a product category has no thumbnail. Carbon Based Auto Category Thumbnails for WooCommerce uses a product image from that category instead, and leaves categories that already have a thumbnail alone.
Requires WooCommerce. Settings are under Carbon Based > Auto Category Thumbnails.
Setup and settings are covered in the Auto Category Thumbnails user guide.
Other plugins for WooCommerce and WordPress stores from Carbon Based Studio.
Free
Premium