Captcha Nedir?
Captcha genelde her yerde karşımıza çıkan bir uygulamadır.Bazen soru şeklinde bazende karakterler şeklinde karşımıza çıkar.Çoğu yerde görmüşsünüzdür Türkiyenin başkenti neresidir? yada Resimdeki sayıları kutucuğa girin şeklinde.
Captcha genelde üye olma,üye girişi yada yorum yazma sayfalarında karşımıza çıkmaktadır.Bunun asıl amacı sitenize gelen botların birden fazla girişimde bulunmasını engellemektedir.İşte bu yüzden captchanin önemi çok büyüktür.
Öncelikle form.php adından bir dosya açıyoruz
< ?php
session_start();
if( isset($_POST['submit'])) {
if( $_SESSION['security_code'] == $_POST['security_code'] && !empty($_SESSION['security_code'] ) ) {
// Insert you code for processing the form here, e.g emailing the submission, entering it into a database.
echo Thank you. Your message said .$_POST['message'].;
unset($_SESSION['security_code']);
} else {
// Insert your code for showing an error message here
echo Sorry, you have provided an invalid security code;
}
} else {
?>
<form action=form.php method=post>
<label for=name>Name: </label><input type=text name=name id=name /><br />
<label for=email>Email: </label><input type=text name=email id=email /><br />
<label for=message>Message: </label><textarea rows=5″ cols=30″ name=message id=message></textarea><br />
<img src=CaptchaSecurityImages.php?width=200&height=80&characters=5″ /><br />
<label for=security_code>Security Code: </label><input id=security_code name=security_code type=text /><br />
<input type=submit name=submit value=Submit />
</form>
< ?php
}
?>Daha sonra CaptchaSecurityImages.php dosyası açıyoruz< ?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++;
}
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);
$_SESSION['security_code'] = $code;
}
}
$width = isset($_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);
?>Hepsi bu kadar.Yukarıda anlatılan uygulamanın çalışır halini indirmek için buraya tıklayın.Kaynak:burakturali
