« File uploading with PHPPut watermark on images using PHP »

Captcha image verification Posted in PHP Tutorials | 238 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.

238 Replies to "Captcha image verification"

charanjeet July 12, 2015 at 7:57 pm | Reply


plz display the view of code working
jj January 20, 2015 at 8:16 am | Reply


hello January 18, 2015 at 4:00 pm | Reply


sa fasdfasdf
jhgh January 16, 2015 at 11:52 am | Reply


kyawswarwin January 15, 2015 at 12:17 pm | Reply


THis example is not work and found a error
Parse error: syntax error, unexpected '$image_p' (T_VARIABLE) in C:\xampp\htdocs\vercap\index.php on line 8
help me bro and sis
admin January 12, 2015 at 2:54 pm | Reply


govind September 6, 2014 at 10:53 am | Reply


A next generation captcha solution

Dips May 29, 2014 at 3:17 pm | Reply


please help me... how to implement captcha & how to store captcha in php database with php coding please......
vinod May 15, 2014 at 8:41 am | Reply


Hi ,

I want to add captcha in my cform , but I failed to understand how to add your code in my php form. pls help.

Here is my form code


* Variables you can change

$cc = "";
$bcc = "";
$headermail = 'xxx@xyz.com';
$toaddress = "xxx@xyz.com";
$email = $_POST['email'];
$name = $_POST['name'];

* do not modify anything below unless you know PHP/HTML/XHTML

function validateEmail($email)
if(eregi('^[a-zA-Z0-9._-]+@[a-zA-Z0-9-]+.[a-zA-Z]{2,4}(.[a-zA-Z]{2,3})?(.[a-zA-Z]{2,3})?$', $email))
return true;
return false;

if(strlen($_POST['companyname']) < 1 || strlen($_POST['name']) < 1 || strlen($_POST['city']) < 1 || strlen($_POST['comments']) < 1 || validateEmail($email) == FALSE)

$emailerror .= '<li>Please enter Your Comapny Name</li>';

else if(!isset($_POST['logodesign'])){
$emailerror .= '<li>Please select any item</li>';

else if(empty($_POST['name'])){
$emailerror .= '<li>Please enter Your Name</li>';

else if(empty($_POST['phone'])){
$emailerror .= '<li>Please enter Your Phone Number</li>';

else if(!is_numeric($_POST['phone'])){
$emailerror .= '<li>Attention! Phone number can only contain digits.</li>';

else if(empty($_POST['email'])){
$emailerror .= '<li>Please enter a valid email address.</li>';

else if(validateEmail($email) == FALSE){
$emailerror .= '<li>Attention! This is invalid E-mail Address. Please try again.</li>';

else if(empty($_POST['city'])){
$emailerror .= '<li>Please enter Your City</li>';

else if(empty($_POST['comments'])){
$emailerror .= '<li>Please enter Your Comments</li>';



$emailerror .= "Your email has been sent successfully";

foreach($_POST['logodesign'] as $value) {
$logo_check .= "<br>$value<br>";

$message = '<!DOCTYPE HTML>
<tr><td>Company Name:</td><td>' . $_POST['companyname'] . '</td></tr>
<tr><td>Logo Package:</td><td>' . $logo_check . '</td></tr>
<tr><td>Name:</td><td>' . $_POST['name'] . '</td></tr>
<tr><td>Email:</td><td>' . $_POST['email'] . '</td></tr>
<tr><td>Phone:</td><td>' . $_POST['phone'] . '</td></tr>
<tr><td>City:</td><td>' . $_POST['city'] . '</td></tr>
<tr><td>Message:</td><td>' . $_POST['comments'] . '</td></tr>

$message = trim(stripslashes($message));

$e_subject = 'Contacted by ' . $name . '.';

$headers = "From: $headermail" . PHP_EOL;
$headers .= "Reply-To: $email" . PHP_EOL;
$headers .= "MIME-Version: 1.0" . PHP_EOL;
$headers .= "Content-type: text/html; charset=utf-8" . PHP_EOL;
$headers .= "Content-Transfer-Encoding: quoted-printable" . PHP_EOL;

mail($toaddress, $e_subject, $message, $headers);


<div id='emailerror'>
<p><? echo $emailerror; ?></p>

<?php /*?>
savi April 25, 2014 at 10:51 am | Reply


my captcha images get refresh though i am entering the same captha value it is showing invalid code

<td class="form-txt" nowrap="nowrap">
<div align="right">Type verification image<font color="red">*</font>:</div>
<td colspan="3" class="form-txt1" nowrap="nowrap">
<img src="verificationimage.php" alt="verification image, type it in the box" width="50" height="24" align="absbottom" id="myCaptcha"/>
<input name="verif_box" type="text" id="verif_box" class="myInput" errMsg="Please Type Valid Code"/></td>
<div class="myArea">

and capthca.php

//header('Content-type: image/jpeg');
$width = 50;
$height = 24;
$my_image = imagecreatetruecolor($width, $height);
imagefill($my_image, 0, 0, 0xFFFFFF);
for ($c = 0; $c < 40; $c++)
$x = rand(0,$width-1);
$y = rand(0,$height-1);
imagesetpixel($my_image, $x, $y, 0x000000);
$x = rand(1,10);
$y = rand(1,10);
$rand_string = rand(1000,9999);
imagestring($my_image, 5, $x, $y, $rand_string, 0x000000);

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 ~