Captcha - Stop spam on your blog, forum or any PHP based websites
A CAPTCHA (IPA: /?kęp?t??/) is a type of challenge-response test used in computing to determine whether the user is human. “CAPTCHA” is a contrived acronym for “Completely Automated Public Turing test to tell Computers and Humans Apart”, trademarked by Carnegie Mellon University. A CAPTCHA involves one computer (a server) which asks a user to complete a test. While the computer is able to generate and grade the test, it is not able to solve the test on its own. Because computers are unable to solve the CAPTCHA, any user entering a correct solution is presumed to be human.
- Wikipedia
We present you one simple way to implement Captcha with PHP & GD Library.
Simple and quick PHP solution for implemet CAPTCHA:
1) Make a PHP script which will generate a CAPTCHA image:
session_start(); header("Expires: Mon, 26 Jul 1997 05:00:00 GMT"); header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT"); header("Cache-Control: no-store, no-cache, must-revalidate"); header("Cache-Control: post-check=0, pre-check=0", false); header("Pragma: no-cache"); function _generateRandom($length=6){ $_rand_src = array( array(48,57) //digits , array(97,122) //lowercase chars // , array(65,90) //uppercase chars ); srand ((double) microtime() * 1000000); $random_string = ""; for($i=0;$i<$length;$i++){ $i1=rand(0,sizeof($_rand_src)-1); $random_string .= chr(rand($_rand_src[$i1][0],$_rand_src[$i1][1])); } return $random_string; } $im = @imagecreatefromjpeg("captcha.jpg"); $rand = _generateRandom(3); $_SESSION['captcha'] = $rand; ImageString($im, 5, 2, 2, $rand[0]." ".$rand[1]." ".$rand[2]." ", ImageColorAllocate ($im, 0, 0, 0)); $rand = _generateRandom(3); ImageString($im, 5, 2, 2, " ".$rand[0]." ".$rand[1]." ".$rand[2], ImageColorAllocate ($im, 255, 0, 0)); Header ('Content-type: image/jpeg'); imagejpeg($im,NULL,100); ImageDestroy($im); ?>
2) Add the following line at the top of the page where you need to implement the CAPTCHA (there should not be any output before this line, except you use php functions ob_start() and ob_end_flush() to turn on output buffering):
3) Add the following line for check is CAPTCHA entered by visitor valid, before the line where you will proceed submitted message:
{ //CAPTHCA is valid; proceed the message: save to database, send by e-mail ... echo 'CAPTHCA is valid; proceed the message'; } else { echo 'CAPTHCA is not valid; ignore submission'; }
?>
4) Finaly add the CAPTCHA to the form:
P.S.
- you may download original article and code sample here: free download php captcha demo
- requirements: a webserver (windows or linux no matter) with PHP engine, with GD (graphic library) support, you may check your php settings with phpinfo() function
- you need some blank jpg image for use it as background for CAPTCHA string
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