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I know this was answered already and points accepted, but I wanted to second Mollom. It was created by the creator of Drupal, and it's not obtrusive. That is, it doesn't even present a CAPTCHA unless it thinks the submission is spam. In my experience, it's been 100% effective, although the actual effectiveness can vary depending on your site, of course.<br />
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It's got a heck of a lot of interfaces as well. Just for reference (and future searchers) here is the URL:<br />
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<a href="http://mollom.com/download" rel="ugc">http://mollom.com/download</a><br />
<br />
Mike<br />

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I know this was answered already and points accepted, but I wanted to second Mollom. It was created by the creator of Drupal, and it's not obtrusive. That is, it doesn't even present a CAPTCHA unless it thinks the submission is spam. In my experience, it's been 100% effective, although the actual effectiveness can vary depending on your site, of course.

It's got a heck of a lot of interfaces as well. Just for reference (and future searchers) here is the URL:

http://mollom.com/download [http://mollom.com/download]

Mike


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I need to put on our website the ability to force someone sending us an email to type in 4 or 5 random characters to confirm that it's human generated.<br />
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For some reason, I cannot remember what this technique is called. <br />
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All pages are in php, so a php version would be helpful.
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I need to put on our website the ability to force someone sending us an email to type in 4 or 5 random characters to confirm that it's human generated.

For some reason, I cannot remember what this technique is called. 

All pages are in php, so a php version would be helpful.

Forcing human creation of emails

PHP is a widely-used server-side scripting language especially suited for web development, powering tens of millions of sites from Facebook to personal WordPress blogs. PHP is often paired with the MySQL relational database, but includes support for most other mainstream databases. By utilizing different Server APIs, PHP can work on many different web servers as a server-side scripting language.