How to Create Captcha in PHP

Introduction

In this article, I describe how to create a Captcha in PHP. Such as when we submit a form a Captcha is often used. A Captcha is an image that is like a verification code. I am using a simple Captcha image without any other custom font to create an image or code. The Captcha code is stored in a session variable. We are using the session variable "cap_code" for the code the user entered and compare it to the session variable. A Captcha is a smartly blurred image and a Captcha code avoid spam and auto submissions. In this article, I am using "css" and "jquery" for additional functionality.

The $_SESSION[variable] creates the original Captcha code and $_POST['captcha'] - Captcha create a code and user enter the code in text box.

Example

This file is "captcha.php":

<?php

//session start

session start();

// calculates the MD5 hash of a string

$Str = md5(microtime());

//substr is a string function

$Str = substr($Str, 0, 6);

//cap_code is a session variable

$_SESSION['cap_code'] = $Str;

//cap_bg is image

$newImage = imagecreatefromjpeg("cap_bg.jpg");

$txtColor = imagecolorallocate($newImage, 0, 0, 0);

imagestring($newImage, 5, 5, 5, $Str, $txtColor);

header("Content-type: image/jpeg");

imagejpeg($newImage);

?>

Simply create a HTML form and include the jQuery code in the head section jQuery uses for validaion. I am using "CSS/JQuery"; I used that just for an extra enhancement.

<?php

//session start here

session_start();

$cap = 'notEq';//this variable use for message

if ($_SERVER['REQUEST_METHOD'] == 'POST')

{

if ($_POST['captcha'] == $_SESSION['cap_code'])

{

// Code is Correct. Do something here!

$cap = 'Eq';

}

else

{

// Code is wrong. Take other action

$cap = '';

}

}

?>

<html>

<head>

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script>

<script type="text/javascript">

$(document).ready(function () {

$('#submit').click(function () {

var name = $('#name').val();

var msg = $('#msg').val();

var captcha = $('#captcha').val();

if (name.length == 0) {

$('#name').addClass('error');

}

else {

$('#name').removeClass('error');

}

if (msg.length == 0) {

$('#msg').addClass('error');

}

else {