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Ask HN: Whats the best captcha service

My website is being bombarded by registration spam and as much as I don't like to do it, I will have to setup a captcha to stop the automated registrations. I know the captcha will have some effect on the conversion rate for real users - but I don't think this can be avoided.

What do you guys think is the best captcha service which does not add too much of a barrier to user registrations?

( 7 comments | 5 points | on HN )
Re:Ask HN: Whats the best captcha service by ozh on Tuesday February 19, 2013 @04:32AM (#5243452)
Anything but reCaptcha. I'm pretty sure I'm a completely legit human, yet I can't decypher recaptcha 95% of the time. This is the biggest turn down of the whole interweb.
Re:Ask HN: Whats the best captcha service by Meltdown on Tuesday February 19, 2013 @10:50AM (#5244859)
Just use a a challenge/response question.

What is the hottest season? What is the coldest season? Capital city of the UK? What are the last three letters of the capital city of the UK?

.. and so on.

Better still to select a question specific to your usergroup.

Regards Melt

Re:Ask HN: Whats the best captcha service by webstartupper on Wednesday February 20, 2013 @02:54AM (#5249423)
I guess you mean something like http://textcaptcha.com/ - any feedback on this service?
Re:Ask HN: Whats the best captcha service by devonbarrett on Tuesday February 26, 2013 @11:44AM (#5286666)
I really like these guys (http://solvemedia.co.uk/index.html) I think it just makes it more interesting... and hey you may even make a bit off it. But I think reCaptcha is becoming impossible to solve
Re:Ask HN: Whats the best captcha service by webstartupper on Wednesday February 20, 2013 @04:00AM (#5249551)
Has anyone used http://textcaptcha.com/ or a similar service? I really like the idea - a self hosted solution would be great.
Re:Ask HN: Whats the best captcha service by dotmanish on Tuesday February 19, 2013 @12:53AM (#5242867)
You may try Google's reCAPTCHA.
Re:Ask HN: Whats the best captcha service by varunkho on Tuesday February 19, 2013 @01:08AM (#5242905)
Please please don't use google recaptcha at least for audio, it is completely unintelligible [0]. I think speech parsing is an easy problem compare to CV for computers that's why recaptcha audio has been made difficult to the point that both (or at least) human and computer alike cannot understand it. Machines have passed turing Test in speech it seems.

[0]: https://groups.google.com/forum/?fromgroups#!topic/recaptcha...

Edit: Never assume that a person with audio recaptcha need would not be visiting your site; people with different needs are more daring and frequent on internet than in real world.