crazy lazy the_post_thumbnail() wrapper (quick & dirty)

functions.php

<?php
function get_the_lazy_post_thumbnail($post_id = 0, $size = '', $attr = array())
{
    if(!intval($post_id))
        $post_id = get_the_ID();

    $thumb = get_the_post_thumbnail($post_id, $size, $attr);

    preg_match('~ src="(.*)" ~isU', $thumb, $result);
    if(count($result) < 2) return $thumb;
    $url = $result[1];

    $new_thumb = preg_replace('~ src="(.*)" ~isU', ' src="data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==" data-src="'.$url.'" ', $thumb);
    $new_thumb = preg_replace('~ height="(.*)" ~isU', ' height="\1" style="max-height:\1px;" ', $new_thumb);
    $new_thumb = str_replace(' class="', ' class="crazy_lazy ', $new_thumb);

    return $new_thumb.'<noscript>'.$thumb.'</noscript>';
}

function the_lazy_post_thumbnail($size = '', $attr = array())
{
    echo get_the_lazy_post_thumbnail(get_the_ID(), $size, $attr);
}