need some help to add some captcha contact form - php

Question

Hi I'm new to PHP and I would like some help please.
I 've created a contact form and i would like to add some captcha. I have created some gif images, that have numbers with some noise added on, and named the code_01.gif for no1, code_02.gif for no2 etc etc. I have put some of them on my form, staticly, for display purposes like this:
<img src="images/code_01.gif" />
<img src="images/code_07.gif" />
<img src="images/code_01.gif" />
<img src="images/code_08.gif" />
<img src="images/code_03.gif" />
<img src="images/code_07.gif" />
<input name="captcha" type="text" id="captcha" />
I would like to add some functionality to display randomly the image codes every time and also check to see if the input matches with the 6 digits that displayed.
Any help would be appreciated.

Answer 1

Simple PHP Captcha
This is one of the easiest CAPTCHA scripts you will ever use. While it doesn’t obscure the text, it will serve its purpose well for many people who need a low-level CAPTCHA solution. This script requires little-to-no setup. The only dependency is the PHP GD library.
It can be as simple as this to use, but it is also configurable:
<?php
session_start();
include("captcha.php");
$_SESSION['captcha'] = captcha();
echo '<img src="' . $_SESSION['captcha']['image_src'] . '" alt="CAPTCHA" />';
?>
Demo: http://labs.abeautifulsite.net/simple-php-captcha/

Answer 2

You can also use this: Securimage
Securimage is an open-source free PHP CAPTCHA script for generating complex images and CAPTCHA codes to protect forms from spam and abuse. It can be easily added into existing forms on your website to provide protection from spam bots. It can run on most any webserver as long as you have PHP installed, and GD support within PHP. Securimage does everything from generating the CAPTCHA images to validating the typed code. Audible codes can be streamed to the browser with Flash for the vision impaired.

Answer 3

Here is a simple math captha type thing I found long ago.
Advantages:
- No Images so less bandwidth usage.
- No external dependency.
FLOW PROCESS
In form.php:
Select one random number $n1
Select another random number $n2
Compute $n1 & $n2 with various math oprations and store it as $result, so that the resulant number is unpredicatble & unaligned with $n1+$n2
Echo "What is $n1 + $n2?"
Ask user to input the answer of question asked in step 4.
Add $result as hidden value in the form.
On submit, the $_POST values are processed by check.php.
In check.php:
If $_POST["answer"] is set, store it in $answer
Compute the $answer in same manner as it was computed in step 3 of form.php
Now, if $answer is equal to $_POST["result"], it is verified that User is Human.
Keep in mind that $answer is answer submitted by user & $result is our result after doing math operations on the $answer.
CODE:
File:form.php
<?php
$n1 = rand(1,15);
$n2 = rand(1,15);
//start making our result unpredictable & non-aligned with hidden value
$result = $n1+$n2;
$result = ($result*3)-2;
$result = ($result+4)*5;
$question="what is $n1 + $n2?";
?>
<form method="post" action="check.php">
<?php echo $question.PHP_EOL; ?>
<input name="answer" type="text"><br />
<input type="hidden" name="result" value="<?php echo $result; ?>">
</form>
File:check.php
<?php
if(isset($_POST["answer")){
$answer = $_POST["answer"];
// start doing same math on $answer
$answer = ($answer*3)-2;
$answer = ($answer+4)*5;
if($answer == $_POST["result"]{
// echo Hurray, you are Human..
// Do anything here..
}else{
echo "Wrong Answer";
}
Logic Implementation at http://codepad.org/2MtULNhZ
The key is in making the encoding & decoding formula harder. So that somebody looking at hidden form value result and Question should not find out the relation in between both of them.