Blocking comment spam without using captcha [closed]

Question

What are some non-captcha methods for blocking spam on my comments?

Answer 1

In my experience the currently most effective methods are honeypot input fields that are made invisible to users via CSS (best use several different methods, such as visibility:hidden, setting a size of 0 pixels, and absolute positioning far outside the browser window); if they're filled anyway you can assume it's a spambot.

This blog describes a rather complex method that I've tried out myself (with 100% success so far), but I suspect that you could get the same result by skipping all the stuff with hashed field names and just add some simple honeypot fields.

Answer 2

1) Adding session-related information into the form Example:

<input type="hidden" name="sh" value="<?php echo dechex(crc32(session_id())); ?>" /> 

then at postback, check whether session is valid or not.

2) Javascript-only. Use Javascript injection at Submission. Example:

<input type="hidden" id="txtKey" name="key" value="" /> <input type="submit" value="Go" onclick="document.getElementById('txtKey').value = '<?php echo dechex(crc32(session_id())) ?>';" /> 

3) Time-limit per IP, User or Session. this is quite straightforward.

4) Randomizing field names:

<?php    $fieldkey = dechex(crc32(mt_rand().dechex(crc32(time()))));    $_SESSION['fieldkey'] = $fieldkey; ?> <input type="text" name="name<?php echo $fieldkey; ?>" value="" /> <input type="text" name="address<?php echo $fieldkey; ?>" value="" />    

Then you can check it over at the server side.