<?php
$categ = $_product->get_categories();
$term = get_term_by ( 'name' , strip_tags($categ), 'product_cat' );
$category_thumbnail = get_woocommerce_term_meta($term->term_id, 'thumbnail_id', true);
$image = wp_get_attachment_url($category_thumbnail);
echo '<img alt="" src="'.$image.'" />';
?>