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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.

<?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>';
};
?>
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243 Comments to "Captcha image verification"

  • suresh

    suresh

    November 19, 2013 at 10:07 am

    First of all i am thankful for your post.! I was fresher in this php feild . i implemented your code .!! it is working properly. But i need capcha validation in same form ..?? how can i valid capcha in same form ..!!! why because whether it is right/wrong it is moving to destination file and there it is showing success/ failure message..!!

  • amol

    amol

    October 21, 2013 at 09:40 am

    i got broken capcha image ...plz .hepl

  • vigneshwaran

    vigneshwaran

    October 3, 2013 at 12:24 pm

    Important
    vignesh
    $vike

  • Ahmadali

    Ahmadali

    July 19, 2013 at 14:24 pm

    please help me... how to store captcha in php mysql with php coding please......

  • Gupta Pedamallu

    Gupta Pedamallu

    June 25, 2013 at 14:27 pm

    thanku.. so much

  • shail

    shail

    June 13, 2013 at 16:23 pm

    i need help on following ....it showing line 4 has a error

    "<?php
    if (!function_exists('bcmodpow'))
    {
    function bcpowmod($x, $y, $mod);{return bcmod(bcpow($x, $y), $mod);};
    }
    ?>


    could you help

  • Parthasarathy

    Parthasarathy

    April 26, 2013 at 15:50 pm

    Please give codes for captcha.php and submit.php fully with example output.

    Thanks.

  • xcer1212

    xcer1212

    March 16, 2013 at 20:35 pm

    to make dirty images :)

    $lines = mt_rand(1,5);



    for( $i=0; $i<$lines; $i++ ) {
    imageline($image_p,
    mt_rand(0,$width), mt_rand(0,$height),
    mt_rand(0,$width), mt_rand(0,$height),
    imagecolorallocate($image_p, mt_rand(150,255), mt_rand(150,255), mt_rand(150,255)));
    }

  • Adebayo Michael

    Adebayo Michael

    March 4, 2013 at 03:19 am

    please help i got a parse error at line 8, Where we have $image_p = imagecreate($width, $height); I checked the previous line and it was ok. please assist. Thanks

  • kalitso

    kalitso

    February 2, 2013 at 17:02 pm

    i cant understand despite un put correct code i receive this error :

    Incorrect verification code ............ :(

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