Posted By

hotdiggity on 07/08/10

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Last Edited at 07/08/10 11:25am

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Invisible Captcha

/ Published in: PHP

Create a textbox that the bot will presume is just a field it can exploit with rubbish and label it with an indicator to let any viewers without the privileges of CSS know that it is to be left blank.

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HTML:
<div class="hidebox">
Please leave blank: <input type="text" id="gotcha" tabindex="-1" name="gotcha" />
</div>

PHP:
<?php
if($_POST["gotcha"]!=""){
header("Location: {$_SERVER[HTTP_REFERER]}");exit;
}
?>

CSS:
.hidebox {
    position:absolute;
    background-color:#CC0000;
    left:0px;
    top:-500px;
    width:1px;
    height:1px;
    overflow:hidden;
}

Note for WordPress:
/wp-content/themes/theme-name/comment.php
add around line 65 (after author,email,url inputs):

<p class="hidefield"><input type="text" name="gotcha" id="gotcha" size="22" tabindex="-1" />
<label for="gotcha"><small><?php _e('Leave blank!'); ?></small></label>
</p>

/wp-comments-post.php
Add after approx. line 54:
$comment_gotcha       = ( isset($_POST['gotcha']) ) ? trim($_POST['gotcha']) : null;

Add after approx. line 87:
if ( $comment_gotcha != '' ) die( __('Error: Your post has been rejected as spam') );

i.e., after

if ( '' == $comment_content )
	wp_die( __('Error: please type a comment.') );

/wp-content/themes/theme-name/style.css
.hidefield { position:absolute; background-color:#CC0000; left:0px; top:-500px; width:1px; height:1px; overflow:hidden; }

URL: http://www.bensky.co.uk/blog/code-tutorials/invisible-capcha-concept-stop-spam-email/

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