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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.

Silkalns

WP Chill

Cristian Raiber

A very useful plugin for everyone using WordPress. Adds reCaptcha security to the WordPress login form, register form and comment form. This plugin could help your blog get rid of a lot of spam comments or brute-force attacks.
Nothing gets passed it if the reCaptcha doesn’t validate.
A few notes about the plugin:
<ul>
<li>Supports audio or image captcha types</li>
<li>Can generate the reCaptcha image / audio type in a number of predefined languages</li>
<li>Adds reCaptcha protection to the WordPress login form</li>
<li>Adds reCaptcha protection to the WordPress register form</li>
<li>Adds reCaptcha protection to the WordPress comment form</li>
<li>Adds reCaptcha protection to the WordPress recover password form</li>
</ul>

Uber reCaptcha

This plugin adds the reCaptcha form to the WordPress login form, recover password form, register form and comment form.

VouchSafe CAPTCHA Replacement vs Uber reCaptcha