Adding additional comment spam protection to sNews, the math/image hybrid captcha

Jan 8th, 2009 at 8:18 am
filed under: sNews CMS / Hacks & Mods

Updated February 25th, 2009, please read this entry for the updated tutorial. Version 2 is vastly improved, it is recommended you upgrade if using version 1.

After waking up this morning to find most all of my articles had a shiny new spam comment, I decided to try out a new method to reduce such annoyances.

This mod will take your math captcha question output and post it as an image, so it remains human readable, but a bot doesn't see the "5 + 6 =" so if they want to hack it, not only does the bot have to decipher the text it will still then have to do the math.

Not a cure-all I'm sure and it won't stop human powered spam (and the key can be decoded and figured out but it's an added annoyance and overhead to bot programmers), but hopefully it'll quell some of the auto spammers that have figured out the basic math captcha.

So let's begin by saving the following code as capgen.php

<?php
$mathkey = "56454669"; // change this to any string of numbers you like
$key     = strip_tags($_GET['key']);
$decode = base64_decode($key);
$keys    = explode($mathkey, $decode);

$x = $keys[0];
$y = $keys[1];

$my_img = imagecreate(80, 20);
imagesavealpha($my_img, true); 
$trans_color = imagecolorallocatealpha($my_img, 0, 0, 0, 127); 
imagefill($my_img, 0, 0, $trans_color);
$text_color = imagecolorallocate($my_img, 0, 0, 0);
imagestring( $my_img, 5, 10, 3, "$x + $y =",
  $text_color);
imagesetthickness ($my_img, 5);

header("Content-type: image/png");
imagepng($my_img);
imagedestroy($my_img);
?>

Make sure to change the math key, now upload that to your public_html folder. OK, back up your snews.php file and then find the function mathCaptcha, and replace it with the following;

// MATH CAPTCHA
function mathCaptcha() {
    $mathkey = "56454669";// make sure keys match!
    $x = rand(1, 9);
    $y = rand(1, 9);
    $_SESSION[_SITE.'mathCaptcha-digit'] = $x + $y;
    $math = '
        <p><label for="calc">
            * '.l('math_captcha').':
        </label><br />';
    //$math .= $x.' + '.$y.' = ';
    $key = base64_encode($x.$mathkey.$y);
    $math .= '<img src="'._SITE.'capgen.php?key='.urlencode($key).'" alt="" />';
    $math .= '
        <input type="text" name="calc" id="calc" />
        </p>';
    return $math;
}

That's it! Now upload your edited snews.php file and you should have basic image generation instead of plain text for the math captcha function. As always, let me know if I left anything out or if you encounter any problems or issues. Yes, I'm using it on my site, just look below, though I'm using a slightly different scheme with multiple keys sprinkled so it can't be pattern matched.

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rated 4/5 (2 votes)

sNews, mods, comments, spam

3 comments

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Matt said:
Jan 8th, 2009 at 9:02 am

This comment is a final test for my math image captcha mod :P

mickey said:
Feb 5th, 2009 at 10:18 am

Great mod! as always :)

Poppoll said:
Feb 11th, 2009 at 5:56 pm

Thanks MDJ
PP

Commenting is closed at this time.

Adding additional comment spam protection to sNews, the math/image hybrid captcha

3 comments

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