I've just heard about "Asirra" and tried it. But, I am a little bit confusing about using. What is your choice for usability?

Asirra or CAPTCHA, and why?

6 Answers 6


CAPTCHA is Completely Automated Public Turing test to tell Computers and Humans Apart. So, indeed, Asirra is (a type of) CAPTCHA... If you mean the warped text type of it, I think Asirra is not useful because:

  • it requires more time than warped text
  • it requires specific interest while trying to fit in a design

I think best type/way is reCaptcha.

  • How do you know it requires more time than warped text? A user study for Asirra suggests it takes 15 seconds to solve a challenge, with 99.6% of users succeeding after two challenges. Jan 27, 2011 at 14:30
  • 3
    not talking about the perception, I am talking about the time you understand the thing... writing a word vs. hovering twelve images and clicking few of them... come on, which requires more time... I will search for a user study of warped text capthca...
    – spinodal
    Jan 27, 2011 at 15:34
  • reCAPTCHA has been pretty much hacked (kind've), and I find it very hard to read. With better hackers, there are harder pictures. With ASIRRA, it's very easy for humans, very difficult for bots, and...IT'S CATS!!! Dec 24, 2013 at 3:34
  • @Markasoftware any proof of that? ReCaptcha exclusively uses OCR failed text, it seems rather unlikely that it's been "hacked" Feb 10, 2014 at 16:51
  • This doesn't seem to have been released to anyone, but: news.vicarious.com/post/65316134613/… Feb 10, 2014 at 23:45

I had never heard of that one, interesting method.

However personally, I find it more user-friendly not to require a captcha (or assira) at all unless there are high enough indications that it might be spam, that way most users are not punished for wanting to interact with the website.

For more ideas, you could check out Can we do better than CAPTCHA? or the article Death to CAPTCHAs as well.


For a blog, or some unofficial fun sites Asirra is OK, but for business sites I would never use it!

  • it requires too much space
  • hardly fits to any design

Personally I would avoid the use of any form of captcha wherever possible - they are a proven factor for form abandonment. There are some nice alternatives discussed here - the "honey pot" one in particular is a great idea.


We conducted a usability test (30 participants), and came to the conclusion that QuizCAPTCHAs rate first in terms of success rate and speed of solving, followed by ReCAPTCHA. Asirra was comparable to ReCAPTCHA, with the odd outcomings that especially elder participants had real difficulties telling cats and dogs apart. So I'd go for a math-based QuizCAPTCHA, or ReCAPTCHA, if you don't mind the Google part.


I have basically the same objection as spinodal - it requires extensive use of a mouse and even if you fail to mark a single picture correctly, it considers you a bot

there is a better alternative - somewhere in the middle between reCaptcha and Asirra

you can use the logic of Asirra and ask user a simple question, such as: what is the next day after Wednesday? - or - enter the next whole number before the number 5

  • Asirra will accept a user who achieves two near-perfect scores; it does not require perfection.
    – supercat
    Dec 19, 2014 at 20:16

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