Questions tagged [captcha]

Captcha is a type of challenge-response test used in computing as an attempt to ensure that the response is given by a human being and not generated by a computer.

CAPTCHA is an acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart".

A CAPTCHA or Captcha is a type of challenge-response test used in computing as an attempt to ensure that the response is not generated by a computer. The process usually involves one computer (a server) asking a user to complete a simple test which the computer is able to generate and grade.

Because other computers are supposedly unable to solve the CAPTCHA, any user entering a correct solution is presumed to be human. Thus, it is sometimes described as a reverse Turing test, because it is administered by a machine and targeted to a human, in contrast to the standard Turing test that is typically administered by a human and targeted to a machine.

The usual reason for using a CAPTCHA is to prevent automated spam from being posted into a public discussion forum or similar site.

A common type of CAPTCHA requires the user to type letters or digits from a distorted image that appears on the screen. However these are becoming increasing unreliable as the automated spam systems that they are trying to defeat are becoming much better at reading the distorted text. More advanced CAPTCHAs are thus becoming available that require the user to answer more detailed questions or perform more complex actions.

Most CAPTCHAs, particularly the more difficult ones, suffer from accessibility issues. The act of making it difficult for an automated system to read and respond to the CAPTCHA also makes it more difficult for many users with disabilities to access sites that use them. For example, a user who relies on a screen reading web browser may be unable to see the CAPTCHA image. Better CAPTCHA systems will provide solutions to some of these issues, such as an audio alternative, but these users are generally still left at a disadvantage.

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Practical non-image based CAPTCHA approaches?

It looks like we'll be adding CAPTCHA support to Stack Overflow. This is necessary to prevent bots, spammers, and other malicious scripted activity. We only want human beings to post or edit things here! We'll be using a JavaScript (jQuery) CAPTCHA…
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How does Google reCAPTCHA v2 work behind the scenes?

This post refers to Google ReCaptcha v2 (not the latest version) Recently Google introduced a simplified "captcha" verification system (video) that enables users to pass the "captcha" just by clicking on it. But how can it differentiate a bot from a…
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Has reCaptcha been cracked / hacked / OCR'd / defeated / broken?

Have any programming methods have been used to defeat reCAPTCHA? I'm interested in seeing evidence and potentially demonstrations that reCAPTCHA in particular has been made obsolete by completely automated, humanless methods. To clarify, not looking…
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ReCaptcha API v2 Styling

I have not had much success finding how to style Google's new recaptcha (v2). The eventual goal is to make it responsive, but I am having difficulty applying styling for even simple things like width. Their API documentation does not appear to give…
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How do I show multiple recaptchas on a single page?

I have 2 forms on a single page. One of the forms has a recaptcha displaying all the time. The other should display a recaptcha only after a certain event such as maxing out login attempts. So there are times when I would need 2 recaptchas to…
oym
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ReCaptcha 2.0: enable Submit button on callback if recaptcha successful

I have a very simple form as follows. I want to make it so that the Submit button is disabled, and only enabled after the user has successfully completed the ReCaptcha. I'm assuming I'm going to need some Javascript / jQuery to do this. Google's…
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Recommendations for java captcha libraries

I'm looking for a replacement for JCaptcha, which doesn't seem to be maintained any more, and isn't very good to begin with. The replacement has to integrate nicely with JavaEE webapps. As I can see it, there are three options: JCaptcha - No longer…
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Blocking comment spam without using captcha

What are some non-captcha methods for blocking spam on my comments?
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How can I avoid google mail server asking me to log in via browser?

I am trying to send emails from Django using an email configured by Google Apps, my configuration at the settings.py file looks something like this: EMAIL_HOST = 'smtp.gmail.com' EMAIL_HOST_USER = 'contact@mydomain.com' EMAIL_HOST_PASSWORD =…
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Recaptcha creates iFrame on page, breaks styling

Recaptcha is adding a "This frame prevents back/forward cache problems in Safari" iFrame to the top of my website (code included below), which is pushing off the styling by 20-30px (approximately). If I set display: none; to the element in Firebug…
Walker
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Vkontakte API using OAuth does not work with Captcha

Vkontakte API rejects requests with Captcha. Here is the example what I do. After the third request I get: Captcha error (14) - Captcha needed. According to documentation it's sufficient to add captcha_sid and captcha_key parameters to the…
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HTTP Status Code for Captcha

Sometimes (when the resource is requested too often) I'm intercepting the presentation of a (HTML) resource with a captcha. The interception doesn't produce any redirection. It happens all at the same URI. I'm wondering now which HTTP status code…
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Easy-to-use django captcha or registration app with captcha?

I want to implement user registration using captcha in Django. The workflow of django-registration app is a great, but it doesn't have captcha. What captcha would you recommend to use with it? Are there some other variants of registration+captcha or…
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How can I bypass the Google CAPTCHA with Selenium and Python?

How can I bypass the Google CAPTCHA using Selenium and Python? When I try to scrape something, Google give me a CAPTCHA. Can I bypass the Google CAPTCHA with Selenium Python? As an example, it's Google reCAPTCHA. You can see this CAPTCHA via this…
user11960891
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rails - Choosing captcha plugin

There are a lot of captchas plugins in Rails and also many types of solutions for preventing spamming and flooding. So it isn't only Rails question. Let's see what types of plugins do we have: 1. Classic image captcha (zendesk's Captcha,…
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