« File uploading with PHPPut watermark on images using PHP »

Captcha image verification Posted in PHP Tutorials | 233 Comments
A good way to avoid automatic form submissions when creating a web form is to add some kind of verification. One of the best ways is to use an image verification, called also captcha. What it does is to dynamically create an image with a random string displayed on it. Then visitor is asked to type that string in a text field and once the form is submitted it checks if the string on the image matches the one inputted by the user. Because there is no easy way to read a text from an image (image recognition) this is a good way to protect your web forms from spammers.
For doing this CAPTCHA I would suggest using a session variable where you store the string generated and displayed on that dynamically generated image.

<?php 
session_start();
$text = rand(10000,99999);
$_SESSION["vercode"] = $text;
$height = 25;
$width = 65;

$image_p = imagecreate($width, $height);
$black = imagecolorallocate($image_p, 0, 0, 0);
$white = imagecolorallocate($image_p, 255, 255, 255);
$font_size = 14;

imagestring($image_p, $font_size, 5, 5, $text, $white);
imagejpeg($image_p, null, 80);
?>


Save this code in a file called captcha.php. What this script does is to generate a random number from 10000 to 99999 and then assign it to $_SESSION['vercode']. Then it generates a 25x65 pixels image with black background and white text using size 14. So if you upload that captcha.php file on your web site and open http://www.site.com/captcha.php you will see an image displaying random integer. You will receive a new random integer every time you refresh that page.

Next we need to create our web form.

<form action="submit.php" method="post"> 
Comment: <textarea name="coment"></textarea><br>
Enter Code <img src="captcha.php"><input type="text" name="vercode" /><br>
<input type="submit" name="Submit" value="Submit" />
</form>


Above code will create a form with a single textarea box, randomly generated image using the captcha.php script and a text field where you will have to enter the verification code.

All we have to do now is to make the submit.php script which will check if the verification code you enter matches the one that has been randomly generated.

<?php 
session_start();
if ($_POST["vercode"] != $_SESSION["vercode"] OR $_SESSION["vercode"]=='') {
echo '<strong>Incorrect verification code.</strong><br>';
} else {
// add form data processing code here
echo '<strong>Verification successful.</strong><br>';
};
?>

Do you know PHP / HTML / CSS / JS well?

Write tutorial on a topic you are good in and become a trusted PHP jabber! Share your experience with millions of other webmasters visiting our website. Contact us for more information how to become a contributor.

233 Replies to "Captcha image verification"

John March 12, 2011 at 3:00 pm | Reply

0

I request to verify my google account.I want to insert the code that was sent to my phone.
tamil March 9, 2011 at 1:14 pm | Reply

0

This captcha coding very useful of my project.
Laura Dakin March 9, 2011 at 12:06 pm | Reply

0

how do i add this to my own form?
cristi March 9, 2011 at 3:46 am | Reply

0

very simple and easy to implement
great!
Thx
Luis March 9, 2011 at 3:01 am | Reply

0

Seens like my script isn\'t saving the SESSION... what to do ?
Luis December 7, 2011 at 11:56 am

0

.... UPS... sorry, I found my mistake. Script is grate and simple!
Kaddy February 28, 2011 at 10:32 pm | Reply

0

@gg to do the same captcha replace rand(10000,99999) with the captcha that you want.
tols12 January 20, 2011 at 7:02 am | Reply

0

I used these codes and they worked great! I have a code to email me when a form is submitted. Here is the code: mail(\"my email\", \"Contact Us Request\", \"Information Requested:\\n\\n$message\", \"From: $email\");. However, even if i enter the wrong verification code, it still emails me. How do i set the verification code not to email me if the code is incorrect? Any help would be appreciated! Thanks!!!
Ryan January 17, 2011 at 2:08 am | Reply

0

This is only working in IE for me, its displaying random garble in chrome and firefox.
Nitish Lamba January 11, 2011 at 1:31 pm | Reply

0

where to save second code started with <form....
and what should be the mane..
Idris Suryadireja December 30, 2010 at 12:22 pm | Reply

0

thanx for script your captcha :))


Please be polite and helpful and do not spam or offend others. We promise you will be treated the same way.

Log in your free account or if you still haven't joined you can create your free account now.

Posting tip:
if you use code in your comments please put it in these tags [php], [sql], [css], [js]
PHP code example: [php] echo date("Y-m-d"); [/php]

Thank you,
~ PHPJabbers team ~