Change default image size

Facebook for WooCommerce seems to using the main uploaded product image when “Use WooCommerce image” is selected.

How would I go about selecting another image size? They are usually called thumbnail, medium , large in WordPress.

I have some custom sizes auto-genereated, for instance woocommerce_single, which crops/extends the image to avoid narrow images of pens, bracelets, etc.

As an example, the Google Feed has a function to do this:

function filter_woocommerce_gpf_image_style( $style ) {
return ‘woocommerce_single’;
}
add_filter( ‘woocommerce_gpf_image_style’, ‘filter_woocommerce_gpf_image_style’ );

Please let me know if you have such a function or setting, in order to avoid modifying the plugin code itself.