captcha ภาษาไทยไม่ตรวจสอบว่าตรงกันหรือไม่อะครับ ปรับยังไงดี???

<?php
session_start();

class CaptchaSecurityImages {

	//var $font = 'monofont.ttf';
	var $font = 'toonregular.ttf';
	//var $font = '/home/www/htdocs/capcha/monofont.ttf'; //ตรวจสอบ path เองมาใส่นะครับ

	function generateCode($characters) {
		/* list all possible characters, similar looking characters and vowels have been removed */
		//$possible = '0123456789';
		$possible = '๑๒๓๔๕๖๗๘๙กขคงฟหด';
		$code = '';
		$i = 0;
		while ($i < $characters) { 
			$code .= substr($possible, mt_rand(0, strlen($possible)-1), 1);
			$i++;
		}
		return $code;
	}

	function CaptchaSecurityImages($width='100',$height='35',$characters='4') {
		$code = $this->generateCode($characters);
		/* font size will be 75% of the image height */
		$font_size = $height * 0.85;
		$image = @imagecreate($width, $height) or die('Cannot initialize new GD image stream');
		/* set the colours */
		$background_color = imagecolorallocate($image, 255, 255, 255);
		$text_color = imagecolorallocate($image, 20, 40, 100);
		$noise_color = imagecolorallocate($image, 120, 255, 0);
		/* generate random dots in background */
		for( $i=0; $i<($width*$height)/3; $i++ ) {
			imagefilledellipse($image, mt_rand(0,$width), mt_rand(0,$height), 1, 1, $noise_color);
		}
		/* generate random lines in background */
		for( $i=0; $i<($width*$height)/150; $i++ ) {
			imageline($image, mt_rand(0,$width), mt_rand(0,$height), mt_rand(0,$width), mt_rand(0,$height), $noise_color);
		}
		/* create textbox and add text */
		$textbox = imagettfbbox($font_size, 0, $this->font, $code) or die('Error in imagettfbbox function');
		$x = ($width - $textbox[4])/2;
		$y = ($height - $textbox[5])/2;
		imagettftext($image, $font_size, 0, $x, $y, $text_color, $this->font , $code) or die('Error in imagettftext function');
		/* output captcha image to browser */
		header('Content-Type: image/jpeg');
		imagejpeg($image);
		imagedestroy($image);

//เข้ารหัสตรงจุดนี้

	//$text_verify=md5($code);
       //session_register("text_verify");
       $_SESSION['security_code'] = $text_verify;

	}

}

$width = isset($_GET['width']) ? $_GET['width'] : '120';
$height = isset($_GET['height']) ? $_GET['height'] : '30';
$characters = isset($_GET['characters']) && $_GET['characters'] > 1 ? $_GET['characters'] : '6';

$captcha = new CaptchaSecurityImages($width,$height,$characters);

?>

	if(copy($q_photo,"$dirphoto/$photo")){
$chrand3= md5($chrand1);                                       //เช็ดตรงนี้
	if($chrand3==$text_verify) {                              //เช็ดตรงนี้
			if($s_name) $post_name=$s_name;//เพิ่มเข้าไปทีหลัง
			$sql="insert into $table_v5_q_webboard values('','$post_topic','$post_message','$photo','$post_name','$post_mail','$post_icq','$q_w','$q_j','$q_n','$q_y','$q_h','$q_i','$req','0','$lasttime','$lasttime','$q_ip','$s_group','$topboard','$chk_email')";
			$re=mysql_query($sql);
			if($re)
			{
			$sql_read="SELECT  * FROM $table_v5_q_webboard where toppic like '$post_topic' and user like '$post_name'";
			$re_read=mysql_query($sql_read);
			$row_read=mysql_fetch_array($re_read);
			}
			
	}//end  if($chrand==$chrand1) {