Preview:
add_action( 'woocommerce_before_shop_loop_item_title', 'add_on_hover_shop_loop_image' ) ; 

function add_on_hover_shop_loop_image() {
  
   $image_id = wc_get_product()->get_gallery_image_ids()[2] ; 
$img_size = wc_get_image_size( $image_id, 'full' );

if ( $image_id ) {

    echo wp_get_attachment_image( $image_id, 'full' ) ;

} else {  //assuming not all products have galleries set

    echo wp_get_attachment_image( wc_get_product()->get_image_id() ) ; 

}
  
  
  
  
  /* CUSTOM ON-HOVER IMAGE */
.woocommerce ul.products li.product a img { 
    /* FORMAT ALL IMAGES TO FILL EQUIVALENT SPACE,
    to remove jitter on replacement 
    height: 629.75px;
	width: 439.98px;*/
    object-fit: cover;
    padding: 0;
    margin: 0 auto;
}
.woocommerce ul.products li.product a img:nth-of-type(2) {
    display: none;
}
.woocommerce ul.products li.product a:hover img:nth-of-type(2) {
    display: block
}
.woocommerce ul.products li.product a:hover img:nth-of-type(1) {
    display: none;
}
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