Tinection 主题中的 Timthumb 如何支持外链图片？

define ('ALLOW_EXTERNAL', TRUE);
define ('ALLOW_ALL_EXTERNAL_SITES', TRUE);

function post_thumbnail( $width = 100,$height = 80 ){
global $post;
if( has_post_thumbnail() ){ //有缩略图，则显示缩略图
$timthumb_src = wp_get_attachment_image_src(get_post_thumbnail_id($post->ID),'full');
$post_timthumb = '<img src="'.get_bloginfo("template_url").'/timthumb.php?src='.$timthumb_src[0].'&h='.$height.'&w='.$width.'&zc=1" alt="'.$post->post_title.'" class="thumb" />';
echo $post_timthumb;
} else{
if ($postid<1)
$postid = get_the_ID();
$image = get_post_meta($postid, "image", TRUE); // 调用自定义域图片
$post_timthumb = '<img src="'.get_bloginfo("template_url").'/timthumb.php?src='.$image.'&h='.$height.'&w='.$width.'&zc=1" alt="'.$post->post_title.'" class="thumb" />';
if ($image != null or $image != '') {
echo $post_timthumb;
} else {
$post_timthumb = '';
ob_start();
ob_end_clean();
$output = preg_match('/<img.+src=[\'"]([^\'"]+)[\'"].*>/i', $post->post_content, $index_matches); //获取日志中第一张图片
$first_img_src = $index_matches [1]; //获取该图片 src
if( !empty($first_img_src) ){ //如果日志中有图片
$path_parts = pathinfo($first_img_src); //获取图片 src 信息
$first_img_name = $path_parts["basename"]; //获取图片名
$first_img_pic = get_bloginfo('wpurl'). '/cache/'.$first_img_name; //文件所在地址
$first_img_file = ABSPATH. 'cache/'.$first_img_name; //保存地址
$expired = 604800; //过期时间
if ( !is_file($first_img_file) || (time() - filemtime($first_img_file))> $expired ){
copy($first_img_src, $first_img_file); //远程获取图片保存于本地
$post_timthumb = '<img src="'.$first_img_src.'" alt="'.$post->post_title.'" class="thumb" />'; //保存时用原图显示
}
$post_timthumb = '<img src="'.get_bloginfo("template_url").'/timthumb.php?src='.$first_img_pic.'&h='.$height.'&w='.$width.'&zc=1" alt="'.$post->post_title.'" class="thumb" />';
} else { //如果日志中没有图片，则显示默认
$post_timthumb = '<img src="'.get_bloginfo("template_url").'/images/default.gif" alt="'.$post->post_title.'" class="thumb" />';
}
echo $post_timthumb;
}
}}

<?php post_thumbnail( 100,100 ) ?>