Good morning!
I added this at functions.php and it worked fine for me:
add_filter( 'post_thumbnail_html', 'my_post_image_html', 10, 3 );
function my_post_image_html( $html, $post_id, $post_image_id ) {
$html = '<a href="' . wp_get_attachment_url( get_post_thumbnail_id($post_id)) . '" title="' . esc_attr( get_post_field( 'post_title', $post_id ) ) . '" rel="lightbox">' . $html . '</a>';
return $html;
}Thank you!
:)
