php 判断gif图片是否为动画图片

<?php 
function IsAnimatedGif($filename) 
{ 
    $fp = fopen($filename, 'rb'); 
    $filecontent = fread($fp, filesize($filename)); 
    fclose($fp); 
   return strpos($filecontent,chr(0x21).chr(0xff).chr(0x0b).'NETSCAPE2.0') === FALSE?0:1; 
} 
echo IsAnimatedGif("test.gif"); 
?>