# Captcha: 
<?php

session_start();



/*

* File: CaptchaSecurityImages.php

* Author: Simon Jarvis

* Copyright: 2006 Simon Jarvis

* Date: 03/08/06

* Updated: 07/02/07

* Requirements: PHP 4/5 with GD and FreeType libraries

* Link: http://www.white-hat-web-design.co.uk/articles/php-captcha.php

* 

* This program is free software; you can redistribute it and/or 

* modify it under the terms of the GNU General Public License 

* as published by the Free Software Foundation; either version 2 

* of the License, or (at your option) any later version.

* 

* This program is distributed in the hope that it will be useful, 

* but WITHOUT ANY WARRANTY; without even the implied warranty of 

* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 

* GNU General Public License for more details: 

* http://www.gnu.org/licenses/gpl.html

*

*/



class CaptchaSecurityImages {



	var $font = 'monofont.ttf';



	function generateCode($characters) {

		/* list all possible characters, similar looking characters and vowels have been removed */

		$possible = '23456789bcdfghjkmnpqrstvwxyz';

		$code = '';

		$i = 0;

		while ($i < $characters) { 

			$code .= substr($possible, mt_rand(0, strlen($possible)-1), 1);

			$i++;

		}
		$_SESSION['security_code'] = $code;

		return $code;

	}



	function CaptchaSecurityImages($width='120',$height='40',$characters='6') {

		$code = $this->generateCode($characters);

		/* font size will be 75% of the image height */

		$font_size = $height * 0.75;

		$image = @imagecreate($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, 100, 120, 180);

		/* 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);

	}



}



$width = isset($_GET['width']) ? $_GET['width'] : '120';

$height = isset($_GET['height']) ? $_GET['height'] : '40';

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



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



?>

# Form.php :
<?php
session_start();
?>
		<img src="CaptchaSecurityImages.php?width=100&height=40&characters=5" /><br />

		<label for="security_code">Security Code: </label><input id="security_code" name="security_code" type="text"  value="<?php echo $_SESSION['security_code']; ?>"/><br />

# What it does is outputs a captcha image with a textfield where is a security code what is not same as text in captcha image, the text in value is a code what was value what was one session back, lets say  i go web
it displays me captcha "HELLO" (image), and outputs field with nothing inside it, now i do refresh:
the captcha is now "YOYOA" and the textfield has now value "HELLO", any suggs?