CAPTCHA which stands for “Completely Automated Public Turing test to tell Computers and Humans Apart” is a type o f challenge-response test to ensure that the response is only generated by humans and not by a computer.
In simple words, CAPTCHA is the word verification test that you will come across the end of a sign-up form while signing up for Gmail or Yahoo account. The following image shows the typical samples of CAPTCHA.
You can make captcha using PHP. Here I am making number
captcha which is achieved by an image. This image text is dynamically create by
php and stored in session. A user can verify whether valid captcha has been
entered or not.
Save this code in named captch.php
<?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);
?>
Index page code
<?php
session_start();
if($_POST["code"]== $_SESSION["vercode"])
$msg="Ok You 're human";
else
$msg="Invalid code";
?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Untitled Document</title>
</head>
<body>
<form action=<?php echo "$_SERVER[PHP_SELF]" ?> method="post">
Enter Code <img src="captcha.php">
<input type="text" name="code" />
<input type="submit" name="ccode" value="Submit" />
<span style="font-size:large;color:#FF0000">
<?php
echo $msg;
?>
</span>
</form>
</body>
</html>
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