Problem: Web form spam or bot induced form submissions is a common issue these days on we pages that have forms. The simplest way to thwart such spam is to use a captcha. There are many varieties of captcha but today I’m going to focus on some simple code that does the job quickly and easily.
Step 1. You need some code to generate a graphical (image) representation of the captcha . Many PHP installations come with GD enabled, we can use this to generate the graphical captcha. We can call this file php_captcha.php and call it from the web page with the form.
<?php
session_start();
$RandomStr = md5(microtime());
$ResultStr = substr($RandomStr,0,5);
$NewImage =imagecreatefromjpeg("img.jpg");
$LineColor = imagecolorallocate($NewImage,233,239,239);
$TextColor = imagecolorallocate($NewImage, 255, 255, 255);
imageline($NewImage,1,1,40,40,$LineColor);
imageline($NewImage,1,100,60,0,$LineColor);
//imagestring($NewImage, 5, 20, 10, $ResultStr, $TextColor);
$font = imageloadfont("font.gdf");
imagestring ($NewImage, $font, 5, 5, $ResultStr, $TextColor );
$_SESSION['key'] = $ResultStr; //store the actual result in a Server session
header("Content-type: image/jpeg");
imagejpeg($NewImage);
?>
Step 2. On the web page with the form simply call this captcha ans use the session information to test its validity. First here’s the web page html code for this simplified form.
<html> <form action="post_form.php" method="post" name="form1"> <img src="php_captcha.php"><br /> <input name="captcha" type="text" id="captcha" size="15"> <br> Please enter the code shown in the image to the left. This is necessary to prevent form spam. <br /> <textarea name="message" cols="25" rows="5"></textarea> <input name="Submit3" type="submit" value="send mail" > <input type="reset" name="Submit22" value="clear"> </form> </html>
Here’s what the sample form looks like
Step 3. Finally on the form processing the submission use something like this to validate the captcha.
<?php
//captcha check
$key=substr($_SESSION['key'],0,5); //session of captcha
$number = $_REQUEST['captcha'];
if($number!=$key)
print_error("<b> The Code you entered does not match the image shown, Press Back and try again! </b>");
?>
Similar one here http://www.abeautifulsite.net/blog/2011/01/a-simple-php-captcha-script/
When the user forward back in their browser the Captcha image fails to load. Can I force it to load when the user goes back?
Great Script so , nice and easy to use and setup! Gracias
Very nice, thanks abrandao.com well done, keep em coming..
I tried but sometimes the image fails to generate , is anyone have this issue
BawlsRice , yeah when the wepage loads for the first time no captcha image shows up, just an image placeholder. If you hit refresh then the proper image shows up. I cannot find anything in the code that will fix this problem. Any thoughts?
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