CAPTCHAs are used to prevent automated software from performing actions.CAPTCHAs have several applications for practical security, including Preventing Comment Spam in Blogs, Preventing Comment Spam in Blogs,CAPTCHAs also offer a plausible solution against email worms and spam.
The following is an example for securing a form with captcha
main.php
<?php
require_once('functions.php');
If($_POST){
If(validate_captcha()){
echo "captcha okay";
//do your actions here
else{
echo " captcha not okay";
}
}
}else{
mt_srand ((double)microtime()*1000000);
$maxran = 1000000;
$random = mt_rand(0, $maxran);
$html = "<html>
<header><title>form with captcha</title></header>
<body> <form name='frm' action='' method='post'>";
$html.="name:<input type='text' name='txtname'>";
$html.="password:<input type='password' name='txtpwd'>";
$html .= "<div id=\"Registercode\"><table><tr><td><img src='". create_captchaImg.php?ran=".$random." ></td> ";
$html .= "<td><input type=\"text\" name=\"captchacode\" maxlength=\"10\" /></td></tr></table></div>";
$html .= "<input type='hidden' name='randomcode' value='". $random."'>
<input type='submit' name='submitbtn' value='submit' >
</form>
";
echo $html;
}
?>
functions.php
<?php
/* function to generate captcha code */
function generate_captcha($num) {
$timemd5=md5($num);
$date = date('F j');
$year=date('Y');
$temp=md5($num . $date.$year . $timemd5);
$capcode = hexdec($temp);
$code = substr($capcode, 4, 6);
return $code;
}
/* function to validate captcha*/
function validate_captcha() {
$captchacode = $_POST['captchacode'];
$randomcode = $_POST['randomcode'];
$generated_code = generate_captcha($randomcode);
$valid = false;
if ((trim($captchacode) != "") && (strcmp($captchacode, $generated_code) == 0))
$valid = true;
else
$valid=false;
return $valid;
}
?>
create_captchaImg.php
<?php
/* function to generate captcha image with the captcha code.choose some image as background */
require_once('functions.php');
$ccode=$_REQUEST['ran'];
$capcode = $ccode;
$code = generate_captcha($capcode);
$image = ImageCreateFromJPEG("images/captchabg.jpeg");//give captcha background image path
$text_color = ImageColorAllocate($image, 80, 80, 80);
Header("Content-type: image/jpeg");
ImageString ($image, 5, 12, 2, $code, $text_color);
ImageJPEG($image, '', 75);
ImageDestroy($image);
}
?>
Thanks for your valued time for writing this informative blog :)
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