PHP如何判断远程图片是否存在

[asp]代码库

<?php
$url2 = 'http://yuncode.net/test.jpg';

$ch = curl_init(); 
$timeout = 10; 
curl_setopt ($ch, CURLOPT_URL, $url2); 
curl_setopt($ch, CURLOPT_HEADER, 1); 
curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1); 
curl_setopt ($ch, CURLOPT_CONNECTTIMEOUT, $timeout); 

$contents = curl_exec($ch);
//echo $contents;
if (preg_match("/404/", $contents)){
	echo '文件不存在';
}
?>