WordPress Newsletter plugin tracking image filter hook

<?php

// WordPress Newsletter plugin tracking image filter hook
// www.tribulant.com

function tracking_image($image = null, $eunique = null) {
    $image = '<img style="display:none;" src="' . home_url() . '/?' . $this -> pre . 'method=track&id=' . $eunique . '" alt="tracking" />';
    return $image;
}

add_filter('newsletters_tracking_image', 'tracking_image', 10, 2);

?>