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Captcha image verification

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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240 Comments to "Captcha image verification"

  • Hello


    October 7, 2015 at 10:39 am


  • devesh


    September 16, 2015 at 08:46 am

    Is there any way to automate the capthca image for API web base or for GUI


  • charanjeet


    July 12, 2015 at 19:57 pm

    plz display the view of code working

  • jj


    January 20, 2015 at 08:16 am


  • hello


    January 18, 2015 at 16:00 pm

    sa fasdfasdf

  • jhgh


    January 16, 2015 at 11:52 am


  • kyawswarwin


    January 15, 2015 at 12:17 pm

    THis example is not work and found a error
    Parse error: syntax error, unexpected '$image_p' (T_VARIABLE) in C:xampphtdocsvercapindex.php on line 8
    help me bro and sis

  • admin


    January 12, 2015 at 14:54 pm


  • govind


    September 6, 2014 at 10:53 am

    A next generation captcha solution


  • Dips


    May 29, 2014 at 15:17 pm

    please help me... how to implement captcha & how to store captcha in php database with php coding please......

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