« File uploading with PHPPut watermark on images using PHP »

Captcha image verification Posted in PHP Tutorials | 239 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.

$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" />

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.

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.

239 Replies to "Captcha image verification"

irctc login July 31, 2012 at 9:20 am | Reply


Really helped me. I will include this in my irctc login page
Talha Mughal July 24, 2012 at 3:32 pm | Reply


This is a great website, where I found helpful material and also found experience good webmaster.
haider ali July 22, 2012 at 10:27 pm | Reply


thanks a lot it really solve my problem
thanks a million
Alex Aalleexx July 3, 2012 at 9:30 am | Reply


Thank a lot!
balavishnu June 6, 2012 at 6:19 am | Reply


Now its working :) Thx for the post
balavishnu June 5, 2012 at 10:05 am | Reply


It says Undefined variable: _SESSION['vercode']; in local host...i copy-paste correctly...pls help me
zzz May 24, 2012 at 9:18 pm | Reply


The image cannot be displayed because it contains error.
I copy and paste it the code.
zzz May 24, 2012 at 9:23 pm


It works now...
Miro April 28, 2012 at 5:59 pm | Reply


Hi , after submiting I get this "Parse error: syntax error, unexpected $end in /home/******/public_html/submit.php on line 1" what is the problem?
lawal leslie temiloluwa April 3, 2012 at 1:14 am | Reply


Ravi March 29, 2012 at 12:57 am | Reply


This is a GREAT Tutorial. Thank you so much for sharing with the world.

I found that even when i type in a incorrect code, the result says "Incorrect validation" but the form gets submitted.

Any idea what could be wrong
Sasho Valkanov March 29, 2012 at 7:55 am


Yes, the form is submitted but you need to place your form processing code within the IF where it says "Verification successful". This way processing code will only be executed if verification code is correct.

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 ~