PHP Captcha

<?php
/*phptext class, version 1.0
created by www.w3schools.in (Gautam kumar)
April 26, 2014
*/
class phptextClass
{
        public function phpcaptcha($textColor,$backgroundColor,$imgWidth,$imgHeight,$noiceLines=0,$noiceDots=0,$noiceColor='#162453')
        {       
                /* Settings */
                $text=$this->random();
                $font = './font/monofont.ttf';/* font */
                $textColor=$this->hexToRGB($textColor);      
                $fontSize = $imgHeight * 0.75;
                
                $im = imagecreatetruecolor($imgWidth, $imgHeight);      
                $textColor = imagecolorallocate($im, $textColor['r'],$textColor['g'],$textColor['b']);                  
                
                $backgroundColor = $this->hexToRGB($backgroundColor);
                $backgroundColor = imagecolorallocate($im, $backgroundColor['r'],$backgroundColor['g'],$backgroundColor['b']);
                                
                /* generating lines randomly in background of image */
                if($noiceLines>0){
                $noiceColor=$this->hexToRGB($noiceColor);    
                $noiceColor = imagecolorallocate($im, $noiceColor['r'],$noiceColor['g'],$noiceColor['b']);
                for( $i=0; $i<$noiceLines; $i++ ) {                          
                        imageline($im, mt_rand(0,$imgWidth), mt_rand(0,$imgHeight),
                        mt_rand(0,$imgWidth), mt_rand(0,$imgHeight), $noiceColor);
                }}                              
                                
                if($noiceDots>0){/* generating the dots randomly in background */
                for( $i=0; $i<$noiceDots; $i++ ) {
                        imagefilledellipse($im, mt_rand(0,$imgWidth),
                        mt_rand(0,$imgHeight), 3, 3, $textColor);
                }}              
                
                imagefill($im,0,0,$backgroundColor);    
                list($x, $y) = $this->ImageTTFCenter($im, $text, $font, $fontSize);  
                imagettftext($im, $fontSize, 0, $x, $y, $textColor, $font, $text);              

                imagejpeg($im,NULL,90);/* Showing image */
                header('Content-Type: image/jpeg');/* defining the image type to be shown in browser widow */
                imagedestroy($im);/* Destroying image instance */
                if(isset($_SESSION)){
                        $_SESSION['captcha_code'] = $text;/* set random text in session for captcha validation*/
                }
        }
        
        /*function to convert hex value to rgb array*/
        protected function hexToRGB($colour)
        {
        if ( $colour[0] == '#' ) {
                        $colour = substr( $colour, 1 );
        }
        if ( strlen( $colour ) == 6 ) {
                        list( $r, $g, $b ) = array( $colour[0] . $colour[1], $colour[2] . $colour[3], $colour[4] . $colour[5] );
        } elseif ( strlen( $colour ) == 3 ) {
                        list( $r, $g, $b ) = array( $colour[0] . $colour[0], $colour[1] . $colour[1], $colour[2] . $colour[2] );
        } else {
                        return false;
        }
        $r = hexdec( $r );
        $g = hexdec( $g );
        $b = hexdec( $b );
        return array( 'r' => $r, 'g' => $g, 'b' => $b );
        }
                
                
        /*function to get center position on image*/
        protected function ImageTTFCenter($image, $text, $font, $size, $angle = 8) 
        {
                $xi = imagesx($image);
                $yi = imagesy($image);
                $box = imagettfbbox($size, $angle, $font, $text);
                $xr = abs(max($box[2], $box[4]))+5;
                $yr = abs(max($box[5], $box[7]));
                $x = intval(($xi - $xr) / 2);
                $y = intval(($yi + $yr) / 2);
                return array($x, $y);   
        }

}
?>

<?php session_start();

if(isset($_POST['Submit'])){
        // code for check server side validation
        if(empty($_SESSION['captcha_code'] ) || strcasecmp($_SESSION['captcha_code'], $_POST['captcha_code']) != 0){  
                $msg="<span style='color:red'>The Validation code does not match!</span>";// Captcha verification is incorrect.             
        }else{// Captcha verification is Correct. Final Code Execute here!              
                $msg="<span style='color:green'>The Validation code has been matched.</span>";              
        }
}       
?>
  
  <form action="" method="post" name="form1" id="form1" >
  <table width="400" border="0" align="center" cellpadding="5" cellspacing="1" class="table">
    <?php if(isset($msg)){?>
    <tr>
      <td colspan="2" align="center" valign="top"><?php echo $msg;?></td>
    </tr>
    <?php } ?>
    <tr>
      <td align="right" valign="top"> Validation code:</td>
      <td><img src="captcha.php?rand=<?php echo rand();?>" id='captchaimg'><br>
        <label for='message'>Enter the code above here :</label>
        <br>
        <input id="captcha_code" name="captcha_code" type="text">
        <br>
        Can't read the image? click <a href='javascript: refreshCaptcha();'>here</a> to refresh.</td>
    </tr>
    <tr>
      <td> </td>
      <td><input name="Submit" type="submit" onclick="return validate();" value="Submit" class="button1"></td>
    </tr>
  </table>
</form>

<?php
        session_start();
        include("./phptextClass.php");  
        
        /*create class object*/
        $phptextObj = new phptextClass();       
        /*phptext function to genrate image with text*/
        $phptextObj->phpcaptcha('#162453','#fff',120,40,10,25);      
 ?>