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Captcha image verification Posted in PHP Tutorials | 228 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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228 Replies to "Captcha image verification"

manoj April 15, 2014 at 9:51 am | Reply


rutenis March 19, 2014 at 11:13 am | Reply


Please help!!! How should look syntax of b.m. submit.php script, when in form entered right captcha code and submit.php must call my formmail.php to send data from form??

if ($_POST["vercode"] != $_SESSION["vercode"] OR $_SESSION["vercode"]=='') {
echo '<strong>Incorrect verification code.</strong>';
} else {
// add form data processing code here
echo '<strong>Verification successful.</strong>';
Dan Flemming March 14, 2014 at 5:32 pm | Reply


I can't get htis script to work.
Can someone help please?

I'm gusessing the "form" is in a .html page.
if not, then that may be the problem.

I get this error:
Parse error: syntax error, unexpected $end in /home/dansmark/public_html/Misc_web-tools/submit.php on line 1
Nasir January 3, 2014 at 8:20 pm | Reply


Good Example working 100%
gg February 28, 2014 at 1:00 pm


yes it works as i expected when i run the program
mudasir November 20, 2013 at 8:10 pm | Reply


i cant understand despite un put correct code i receive this error Why plz Solve problem...
suresh November 19, 2013 at 10:07 am | Reply


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 October 21, 2013 at 9:40 am | Reply


i got broken capcha image ...plz .hepl
vigneshwaran October 3, 2013 at 12:24 pm | Reply


Ahmadali July 19, 2013 at 2:24 pm | Reply


please help me... how to store captcha in php mysql with php coding please......
Gupta Pedamallu June 25, 2013 at 2:27 pm | Reply


thanku.. so much

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