The verification code image cannot be displayed. PHP verification code

Copy the code The code is as follows:

Class code
{
var $width =160; //The width of the image
var $hight =40; //The height of the image
var $image ;
var $red =223; //RGB color of the picture
var $green =225; //Red
var $blue =227; //Green
var $pix =227; //Blue
var $pixcolor; / /various color;
var $pixred = 242; //Red
var $pixgreen = 168; //Green
var $pixblue = 162; //Blue
var $txt=null; //Verification code text
var $ txtcode=null;
var $txtsub=null;
var $pixnum = 300; //Number of miscellaneous points
var $i=0;
var $widthpx=0;
var $highty=0;
var $txtreg=50 ;
var $txtgreen=30;
function createimage() //Create an image and color it
{
$this->image = imagecreate($this->width,$this->hight);
$this->color = imagecolorallocate($this->image,$this->red,$this->green,$this->blue);
return imagefill($this->image,0 ,0,$this->color);
}
function createepix() //Interference factors
{
for($this->i=1;$this->i<$this->pixnum; $this->i++)
{
$this->widthpx = rand(0,$this->width);
$this->highty = rand(0,$this->hight);
$this->pixcolor = imagecolorallocate($this->image,$this->pixred,$this->pixgreen,$this->pixblue);
 imagesetpixel($this->image,$this ->widthpx,$this->highty,$this->pixcolor);
}
}
function gettxt() //Create verification code text
{
$this->txt = array("I" , "love", "you", "ye", "just", "wisdom", "ming", "fa", "true", "of", "very", "think", "no"," Zhi", "to", "for", "what", "what", "just", "yes", "forget", "no", "er", "you", "ye", "Xu" ,"shang","generation","owe","money");
for($this->i=0;$this->i<6;$this->i++)
{
$ this->sub = $this->txt[rand(0,29)];
$this->txtcode.= $this->sub;
}
$this->txtcode = iconv(" GB2312","UTF-8",$this->txtcode);
$_SESSION["code"] = $this->txtcode; //Generated verification ID
}
function createstring() //Create verification Code picture
{
imagettftext($this->image,20,5,0,40,$this->pixcolor,"C:WINDOWSFontssimsun.ttc ",$this->txtcode);
header("content -type:image/png");
return imagepng($this->image);
imagedestroy($this->image);
}
function getcodeimage()//Get the verification code image
{
$this ->createimage();
$this->gettxt();
$this->createpix();
$this->createstring();
}
}
?>
session_start();
$text = new code;
$text->createimage();
$text->gettxt();
$text->createpix();
$text->createstring( );
?>

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