[求助]如何解决php编程中的如下问题

<?php
Header("Content-type:image/gif");
$string=implode($argv,"");
$im=imagecreatefromgif("2.gif");
$orange=ImageColorAllocate($im,220,210,60);
$px=(imagesx($im)-7.5*strlen($string))/2;
ImageString($im,3,$px,9,$string,$orange);
ImageGif($im);
ImageDestroy($im);
?>


Warning: Cannot modify header information - headers already sent by (output started at F:\qingwa\php\index.php:8) in F:\qingwa\php\index.php on line 9
请问这个问题怎么解决