As the inaugural post of the NuCaptcha blog I thought I would start with describing, at a high level, the two primary types of Captchas.

All Captchas are a form of challenge-response authentication. That is to say, you are asked a question, you respond, and if you’re correct, access is granted. You’re unlocking a password.

What makes a Captcha different than a password is the type of question. For a password the question is “Do you know the magic words?” “Yes, it’s Open Sesame.” Anyone who knows the magic words gets through.

Captchas are most often used to ensure the user is human. To do this effectively we need to come up with a question that humans can answer easily, and software cannot. The earliest and most common type of Captchas are transcription based Captchas.

In a transcription based Captcha the user is usually shown an image with some text on it. They must simply copy the text.

A significant advantage of a transcription based Captcha is that it’s very easy to understand. Directions can be as few as three words: “type the letters”. It is so easy to understand they are used the world over with little modification. They are also quick interactions. Most transcription based Captchas take less than 10 seconds to complete.

The alternative to transcription based Captchas are test based Captchas.

In a test based Captcha the user is given a test they must pass. They are shown the test, they need to think about it, and then come up with the answer.

Test based Captchas have been around several years with little success. Even giants such as Microsoft have given it a try (Asirra) and have failed.

Beyond the challenges of creating a secure test based Captcha is communicating what is expected. If there is any ambiguity in the directions or the expected answer, users may feel frustrated and unsure. Moreover, the test draws the users focus away from the action they’re trying to take on the website, especially as test completion time and complexity grows.

With an estimated 6 billion Captchas used per month, you’ve probably seen one recently, and it was probably a transcription based Captcha. Our hope is that soon most of those Captchas will be NuCaptchas. Why do we think this is achievable? NuCaptcha tests are harder to break for non-humans, yet easier (and more fun) for humans, primarily due to one unique attribute: motion. Please check out a few of the Captcha videos on our site and see for yourself: www.nucaptcha.com.