请大家帮我想想，附加码不能显示是怎么回事呀？

请大家帮我看看：）<td colspan="2" align=center>*请在附加码框输入<img src="img.php?text=<? echo $text; ?>&localtime1=<? echo $localtime1; ?>"></td>img.php中：
Header( "Content-type: image/gif"); 
if(!isset($s)) $s=11; $text=AddCode($text,$localtime1,4);$size = imagettfbbox($s,0, "img/Verdanab.ttf",$text); 
//设定长宽 
$dx = abs($size[2]-$size[0]); 
$dy = abs($size[5]-$size[3]); 
$xpad=9; 
$ypad=9; $im = imagecreate($dx+$xpad,$dy+$ypad); 
//设定R,G,B 
$blue = ImageColorAllocate($im, 255,255,255); $black = ImageColorAllocate($im, 0,0,0); 
$white = ImageColorAllocate($im, 0,0,0); 
//画图 
//ImageRectangle($im,0,0,$dx+$xpad-1,$dy+$ypad-1,$black); 
//ImageRectangle($im,0,0,$dx+$xpad,$dy+$ypad,$white); 
ImageTTFText($im, $s, 0, (int)($xpad/2)+1, $dy+(int)($ypad/2), $black, "img/Verdanab.ttf", $text); 
//ImageTTFText($im, $s, 0, (int)($xpad/2), $dy+(int)($ypad/2)-1, $white, "image/Verdanab.ttf", $text); 
imagepng($im); ImageDestroy($im); 
?>