Rewrite of the WordPress "get_the_post_thumbnail" for compatibility with jQuery LazyLoad plugin

lazyload-get-the-post-thumbnail.php

<php
// Rewrite of "get_the_post_thumbnail" for compatibility with jQuery LazyLoad plugin
function my_get_the_post_lazyload_thumbnail( $post_id = false, $size = 'full' ) {
	if ( $post_id ) {
		// Get the id of the attachment
		$attachment_id = get_post_thumbnail_id( $post_id );
		if ( $attachment_id ) {
			$src = wp_get_attachment_image_src( $attachment_id, $size );
			if ($src) {
				$img = get_the_post_thumbnail( $post_id, $size, array(
					'class' => 'lazy',
					'data-original' => $src[0],
					'src' => get_stylesheet_directory_uri() . '/lib/images/transparent.png'
				) );
				return $img; // returns image tag string or '' (empty string)
			}
		}
	}
	return false; // missing either: post_id, attachment_id, or src
}

// Echos out "my_get_the_post_lazyload_thumbnail" function
function my_the_post_lazyload_thumbnail( $post_id, $size ) {
	echo my_get_the_post_lazyload_thumbnail( $post_id, $size );
}
?>