php验证码有关问题

php验证码问题
linux下php5 安装了php5-gd，但是验证码图片还是不能显示求解为何？


图片显示为这样




img.php

PHP code

<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--><?phpsession_start ();$width=50;$height=20;header("Content-type:image/gif");$randval=randStr(4);$im=imagecreatetruecolor($width,$height);$r=array(255,215,235,195,175);$g=array(255,215,235,195,175);$b=array(255,215,235,195,175);$key=rand(0,4);$backColor=imagecolorallocate($im,$r[$key],$g[$key],$b[$key]);$pointColor=imagecolorallocate($im,255,170,255);imagefill($im,0,0,$backColor);$stringColor=imagecolorallocate($im,0,0,0);for($i=0;$i<=100;$i++){    $pointX=rand(2,$width-2);    $pointY=rand(2,$height-2);    imagesetpixel($im,$pointX,$pointY,$pointColor);}imagestring($im,3,5,1,$randval,$stringColor);$ImageFun='Imagegif';$ImageFun($im);imagedestroy($im);function randStr($len=10){    $chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';    $string="";    while(strlen($string)<$len){        $string.=substr($char,(rand()%strlen($chars)),1);    }    return $string;}$_SESSION['identifying']=$randval;?>

PHP code

<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->?<title>登录</title><meta http-equiv="Content-Type" content="text/html; charset=utf-8"><link href="images/public.css" type="text/css" rel="stylesheet"><link href="images/login.css" type="text/css" rel="stylesheet"><style type="text/css"></style><meta content="MSHTML 6.00.2900.5848" name="GENERATOR"><script language="javascript">function check(){    if(docnument.getElementByID("txtUserName").value==''){        alert("用户名不允许为空");        docnument.getElementById("txtUserName").focus();        return false;    }    if(docnument.getElementById("txtUserPassword").value==''){        alert("密码不能为空");        docnument.getElementById("txtUserPassword").focus();        return false;    }    return true;}</script>    

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