3 More Alternatives to CAPTCHA

If you missed it, Monday’s post explored 6 ways to reduce friction in the prove-you-are-human process. Thanks to our wonderful readers, we have 3 more CAPTCHA alternatives to cover: animated NuCaptcha, gamified Vouchsafe and a tip from “Anton” that we could describe as a “honeypot button.”


NuCaptcha combines video-animated CAPTCHAs with behavioral analysis to improve the user experience while making it tougher for OCR (Optical Character Recognition) programs to decipher.

Video CAPTCHAs show letters moving back and forth, which could be captured as static images by OCR, but overlapping layers are much harder to recognize.

Behavioral analysis takes into account various cues to assess the security risk of a user. Legitimate users are shown easy-to-solve CAPTCHAs, while suspect spammers are given more difficult ones.

NuCaptcha is not free, details on their website.


VouchSafe uses artificial intelligence to generate challenges based on object associations that humans can recognize but bots can’t. For example, drawing a line between two objects that match each other.

Hey, it’s harder than it looks! I couldn’t figure this one out. Despite the fact I got it wrong, the system could recognize I’m human by the interaction of drawing the line.

Honeypot Buttons

One of the tips from the original post was to use a “honeypot field” — a hidden CSS field invisible to humans, but fed to bots. Anton’s comment described a solution that uses 3 buttons with fake input element labels. For example:

“Don’t post this” | “Post this” | “Cancel”

You can catch robots with server-side validation easily because they tend to just “submit.”

Ask Bots to Play Nice

Finally, a bonus method. I can’t believe I forgot about this one

Thanks again to our readers! Any more ideas? Please drop us a comment.

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18 Responses to “3 More Alternatives to CAPTCHA”

  1. bill says:

    Honeypot buttons won’t work – don’t do this. Users who press [Enter] to submit the form will unknowingly submit using the “Don’t post this” button. This is because the browser submits using the first button when you use the keyboard.

    Don’t break basic usability!

    • You could style the don’t post this much smaller than the other 2 to maximize clicks on the right one? I mean, make it really, really tiny? (Or very light gray text on white?)

  2. Hal says:

    What’s the actual answer for the maple one? If I saw that on a site, I’d just leave (pun somewhat intended).

    • I tried a bunch of them out, most of them were very intuitive (though I got another one wrong). I think the mere action of drawing the line should be enough to prove you are human, regardless if the association is correct. I think the other component of VouchSafe is “crowdplay” – teaching its AI how real people make associations between items, though I may not have the correct understanding of how the technology works.

      • thao says:

        Yes I think the maple leaf one is a poor example. They should either make the question easier or just state in the instructions all you need to do is draw a line.

        FYI my guess is the stack of pencils, as school starts in the fall in North America.

  3. Hi Linda,

    I have to admit that I was stumped also by the VouchSafe captcha – unless it is the Maple leaves to the snowman – but if my guess is correct, I think the link between the two objects is somewhat tenuous.

    The trouble with this type of solution is that people non-Canadian resident may find it difficult to answer. Your very candid admission that you had a problem with this one (despite being a Canadian resident in Vancouver), is readily appreciated by me as someone who spent many years in Canada. I was also stumped!

    Is this concept not going too far, as many website visitors may have a problem if they are from a foreign land and do not know the ins and outs of a particular set of images?

    Moving on, I certainly could not answer ‘Ask Bots to Play Nice’, as I have never heard of Littlefoot or ‘Land Before Time’ and am not considered normally a literary ignoramus.

    More thought needed on this one?

    • :) The last one was from one of my favorite geek webcomics. The Land Before Time was a children’s movie back in the 80s or early 90s with cartoon dinosaurs, I understand not everyone would get the cultural reference. So the joke is that bots wouldn’t cry at anything sentimental, but all humans would. The bots are asked to not lie about having feelings to pass the security test ;-)

  4. Great post Linda. Thought I’d chime in with another creative alternative.

    WebKit has a nice Captcha implementation integrated into their CMS solutions (example is at the bottom of this page: http://www.webkit.com/developers-for-designers.html)

  5. TomN says:

    I did some research into 4D captchas (animated, 3D captchas) and posted the results to a blog.

    The theory is that animated, realistic 3D leverages something humans are evolved to do easily, but computers struggle with.

    (This isn’t a pitch because it was just a side-research project, not a company.)

    usability test site: http://www.vappic.com

    blog: blog.vappic.com

  6. Najiko says:

    It has long been time to say goodbye to captchas!

    “Are you a human” is yet another captcha alternative.

  7. Aditi Datta says:

    Thanks Linda for sharing this lovely post with us!! These 3 more alternatives to Captcha sounds really very interesting. I specially like this NUCaptcha. This post is truly very informative and interesting to read.

  8. Maxime says:

    I believe CAPTCHAS are one thing that everyone hates. Sometimes they are so hard to find out that I just abandon and go somewhere else.

    Imagine all those mentionned previously for a non-english speaker (yes, sometimes people from France, Italy, Spain, etc. buy internationnaly online)…

    In my opinion, best ones are : 2 + 3 = ?

  9. Brian says:

    The best one I have ever seen was a video clip with the characters floating down a stream so the water makes the characters go up an down and not in a straight line, to me it would be
    impossible for a bot. But any human can read them without any problems, even a child would be able to read the characters. Unfortunately although I saved the developer’s name and web address I have no idea where I put it.

    That is very common for me, I very much doubt that happens to anyone else that visits this web site, but then they would not be 70 like me.
    I started in computers 46 years ago and still get as much fun as I did in 1966

  10. Hey, thanks for mentioning VouchSafe. I’ve tweeted out a link to your article.

    Yes, some VouchSafe challenges are tougher than others. It’s a matter or our fine-tuning the AI so it “thinks” more like a human. It also learns from user input.

    We’re hoping to release an updated version of VouchSafe soon, that includes more content and more languages.

    Yours truly,
    Chris Ivey

    • That reminds me of oAuth, it’s a good bot-proof method but have you user tested it to see if people take the 4 steps to get through? What about international users that may not have a good grasp of English?

  11. Kim says:

    You can check this solution – http://www.lirullu.com

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