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<?php
// Add "Click to enlarge image" under procuct thumbnail on single product page
add_action( 'woocommerce_product_thumbnails', 'woocommerce_click_to_enlarge', 10 );
function woocommerce_click_to_enlarge() {
	echo '<a itemprop="image" href="';
	echo wp_get_attachment_url( get_post_thumbnail_id() );
	echo '" class="zoom" rel="thumbnails" title="';
	echo get_the_title( get_post_thumbnail_id() );
	echo '">Click to enlarge image</a>';
}
?>