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Captcha image verification Posted in PHP Tutorials | 232 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>';

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232 Replies to "Captcha image verification"

Mark Jackson May 13, 2007 at 1:58 am | Reply


How do I get the form to email me the results?
Veselin: you can combine this tutorial with <a href='http://www.phpjabbers.com/make-contact-form-and-send-email-in-php-php21.html'>contact form tutorial</a>
jerry jennings May 11, 2007 at 10:51 pm | Reply


Please give us a price on getting bulkconveyors.com/order.html working with captcha
It now works but it transfers data with any number in the verify box
Robert May 9, 2007 at 7:02 pm | Reply


WOW. This script is superb.
angie May 8, 2007 at 12:12 pm | Reply


I have used your scripot and all is working well, however is there a way to make the email address show in the from feild of the incoming email? at the moment i have to copy and past efrom the email feild of the form, would be great if i could just hit reply?
Veselin: this depends on your server configuration. However this <a href='http://www.phpjabbers.com/make-contact-form-and-send-email-in-php-php21.html'>contact form example</a> is done to send emails having the FROM field set to senders email

this part here
$mailheader = "From: ".$_POST["email"]."\r\n";
$mailheader .= "Reply-To: ".$_POST["email"]."\r\n";
Milan May 7, 2007 at 2:43 am | Reply


Hi there;

what is the feee for a code verification PHP script to be embeded in to our form?

Yhank you;

jerry April 26, 2007 at 8:40 pm | Reply


Our form at bulkconveyors.com/ordernew.htm uses your
capture script. The random number generator works but I can use any number in the blank box and the email is delivered.
Can you suggesty a fix ???
Veselin: did you include the if() check in your submitting script
Prateek April 24, 2007 at 12:26 am | Reply


Hello Can i integrate your captcha script on our contact us form. We\\\'re using Autoresponder programs to collect all the field datas to our autoresponder list. please check the form here http://www.bigfootsafari.com/contact/
Omar April 23, 2007 at 5:02 pm | Reply


I like image verification; I use it for downloading my files in my website.
But there is a problem, when I open download page over one window, one page (last one) will accept the code but the rest won\'t because $_SESSION[\"vercode\"] changes everytime I load download page.
Also this problem exists in this current page; try to open it in many windows.
How can I solve it?
Veselin: you can add an if() check if the verification code has already been generated so it does not generate it twice
John Robinson April 21, 2007 at 5:00 pm | Reply


Hello, I would like to change the background colour to an image file, is this possible ?
Veselin: yes, you can do that by using imagecreatefromjpeg()
jerry jennings April 9, 2007 at 4:33 am | Reply


What is your fee to help us get the captcha script runing ?
Veselin Stoilov: usually $20 but it depends on your form

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