https://wordpress.org/plugins/woo-out-of-stock-products/

Developed in 2016 to fill the need of a client request birthed this WordPress plugin with ~6,000 active installs and over 30,000 lifetime downloads.

WordPress plugin link: https://wordpress.org/plugins/woo-out-of-stock-products/

Github repo: https://github.com/amg262/woo-out-of-stock-products

Now your WooCommerce products that are out of stock can be distinguished from in stock products with a dynamically applied image overlay to all product images that are out of stock. You can use the preloaded pictures included in the plugin, or upload and set your own on the plugin settings page.