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VouchSafe is an easy, effective replacement for comment and registration CAPTCHAs that’s highly secure, and easier for your users to complete.
You can use VouchSafe to secure your comments and registration from spam. VouchSafe is easy to use, and very effective in stopping spammers. It’s the first Human Interactive Proof that use an adaptive AI to create challenges that only humans can solve. You can learn more about VouchSafe at the <a href="http://www.vouchsafe.com" rel="nofollow ugc">VouchSafe website</a>.
To solve a challenge, users either draw a line to join two objects that are related, or circle one object that doesn’t belong in a group of related objects.
For visually or motor-impaired users, VouchSafe offers audio-based type-in challenges. VouchSafe is compatible with most smart phones and tablet computers.
VouchSafe requires users to register their domain to get an API key to activate their plugin. Your keyset allows you to customize the way VouchSafe will appear on each domain you manage. VouchSafe also offers support for SSL.
Full installation instructions with screenshots can be found in our <a href="http://www.vouchsafe.com/user-guide-for-wordpress" rel="nofollow ugc">installation guide</a>.
To get an API key to activate VouchSafe on your domain, go to our <a href="http://console.vouchsafe.com" rel="nofollow ugc">registration page</a>.
If you run into trouble <a href="http://www.vouchsafe.com/contact" rel="nofollow ugc">contact us</a> or you can check the posts on our <a href="http://www.facebook.com/vouchsafe.me?sk=app_2373072738" rel="nofollow ugc">Facebook discussion page</a>.

VouchSafe CAPTCHA Replacement

VouchSafe is an easy, effective replacement for comment and registration CAPTCHAs that's highly secure, and easier for your users to complete.

Automattic

Donncha O Caoimh (a11n)

This plugin adds a stylesheet or image to your blog’s html source code. When a browser loads that stylesheet or image a cookie is dropped. If that user then leaves a comment the cookie is checked. If it doesn’t exist the comment is marked as spam. 
The plugin can also check how long it took a user to enter a comment. If it’s too fast it’s probably a spam bot. How fast can a legitimate user enter their name, email, web address and enter a well thought out comment?
For the adventurous, add these lines to your .htaccess and it will block spam attempts before they ever get to WordPress. Replace the Xs with the cookie that was set in your browser after viewing your blog. You can also find the cookie value by examining the page source code and looking for “css.php?k=XXXXXXXXXXXXXXXXXXX”. Make sure the lines go above the standard WordPress rules.
<pre><code> RewriteCond %{HTTP_COOKIE} !^.*XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.*$
 RewriteRule ^wp-comments-post.php - [F,L]
</code></pre>
If you use WordPress MU, replace wp-comments-post.php above with wp-signup.php to block spam signups.
<pre><code> RewriteCond %{HTTP_COOKIE} !^.*XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.*$
 RewriteRule ^wp-signup.php - [F,L]
</code></pre>

Cookies for Comments

If you don't use any other spam filter plugins, then you can rely on this to stop spam comments for sure!

Must have, if you don't use any other spam filters!

I'd been getting a dozen spams a day on two of my sites. We installed "Stop Spam Comments" on one and "Cookies for Comments" on the other. Both worked perfectly. No more spam. Thanks!



very easy and no more spam!

Sets a cookie on a random URL that is then checked when a comment is posted. If the cookie is missing the comment is marked as spam.

VouchSafe CAPTCHA Replacement vs Cookies for Comments