<p>Of all the forms of CAPTCHA available, which one is the "least crackable" while remaining fairly human readable?</p>

[{'answer_id': 59570, 'author': 'Thomas Owens', 'author_id': 572, 'author_profile': 'https://Stackoverflow.com/users/572', 'pm_score': 3, 'selected': False, 'text': "<p>I believe that CAPTCHA is dying. If someone really wants to break it, it will be broken. I read (somewhere, don't remember where) about a site that gave you free porn in exchange for answering CAPTCHAs to they can be rendered obsolete by bots. So, why bother?</p>\n"}, {'answer_id': 59575, 'author': 'rpetrich', 'author_id': 4007, 'author_profile': 'https://Stackoverflow.com/users/4007', 'pm_score': 5, 'selected': True, 'text': '<p>I agree with Thomas. Captcha is on its way out. But if you must use it, <a href="http://www.recaptcha.net" rel="noreferrer">reCAPTCHA</a>  is a pretty good provider with a simple API.</p>\n'}, {'answer_id': 59581, 'author': 'Flory', 'author_id': 5551, 'author_profile': 'https://Stackoverflow.com/users/5551', 'pm_score': 2, 'selected': False, 'text': '<p>This information is hard to really know because I believe a CAPTCHA gets broken long before anybody knows about it.  There is economic incentive for those that break them to keep it quiet.</p>\n\n<p>I used to work with a guy whose job revolved mostly around breaking CAPTCHA\'s and I can tell you the one giving them fits currently is <a href="http://recaptcha.net/" rel="nofollow noreferrer">reCAPTCHA</a>.</p>\n\n<p>Now, does that mean it will forever, call me skeptical.</p>\n'}, {'answer_id': 59583, 'author': 'Chris Upchurch', 'author_id': 2600, 'author_profile': 'https://Stackoverflow.com/users/2600', 'pm_score': 5, 'selected': False, 'text': '<blockquote>\n  <p>I believe that CAPTCHA is dying. If someone really wants to break it, it will be broken. I read (somewhere, don\'t remember where) about a site that gave you free porn in exchange for answering CAPTCHAs to they can be rendered obsolete by bots. So, why bother?</p>\n</blockquote>\n\n<p>Anyone who really wants to break this padlock can use a pair of bolt cutters, so why bother with the lock?<br>\nAnyone who really wants to steal this car can drive up with a tow truck, so why bother locking my car?<br>\nAnyone who really wants to open this safe can cut it open with an oxyacetylene torch, so why bother putting things in the safe?</p>\n\n<p>Because using the padlock, locking your car, putting valuables in a safe, and using a CAPTCHA weeds out a large spectrum of relatively unsophisticated or unmotivated attackers.  The fact that it doesn\'t stop sophisticated, highly motivated attackers doesn\'t mean that it doesn\'t work at all.  Using a CAPTCHA isn\'t going to stop all spammers, but it\'s going to tremendously reduce the amount that requires filtering or manual intervention.  </p>\n\n<p>Heck look at the lame CAPTCHA that Jeff uses on <a href="http://www.codinghorror.com/blog/" rel="noreferrer">his blog</a>.  Even a wimpy barrier like that still provides a lot of protection.</p>\n'}, {'answer_id': 59588, 'author': 'Leahn Novash', 'author_id': 5954, 'author_profile': 'https://Stackoverflow.com/users/5954', 'pm_score': 0, 'selected': False, 'text': "<p>As far as I know, the Google's one is the best that there is. It hasn't been broken by computer programs yet. What I know that the crackers have been doing is to copy the image and then send it to many phishing websites where humans solve them to enter those websites.</p>\n"}, {'answer_id': 59591, 'author': 'Omer van Kloeten', 'author_id': 4979, 'author_profile': 'https://Stackoverflow.com/users/4979', 'pm_score': 2, 'selected': False, 'text': '<p>If you\'re a small enough site, no one would bother.</p>\n\n<p>If you\'re still looking for a CAPTCHA, I like <a href="http://ocr-research.org.ua/teabag.html" rel="nofollow noreferrer">tEABAG_3D</a> by the <a href="http://ocr-research.org.ua/index.html" rel="nofollow noreferrer">OCR Research Team</a>. It\'s complicated to break and uses your 3D vision. Plus, it being developed by people who break CAPTCHAs for fun.</p>\n'}, {'answer_id': 59621, 'author': 'Danimal', 'author_id': 2757, 'author_profile': 'https://Stackoverflow.com/users/2757', 'pm_score': 0, 'selected': False, 'text': '<p>It doesn\'t matter if captchas are broken or not now -- <a href="http://ddanchev.blogspot.com/2008/08/exposing-indias-captcha-solving-economy.html" rel="nofollow noreferrer">there are Indian firms that do nothing but process captchas</a>. I\'m with the rest of the group in saying that Captchas are on their way out. </p>\n'}, {'answer_id': 289406, 'author': 'Etienne', 'author_id': 33584, 'author_profile': 'https://Stackoverflow.com/users/33584', 'pm_score': 0, 'selected': False, 'text': '<p>Here is a cool link to create CAPTCHA..... <a href="http://www.codeproject.com/aspnet/CaptchaImage.asp" rel="nofollow noreferrer">http://www.codeproject.com/aspnet/CaptchaImage.asp</a></p>\n'}, {'answer_id': 289428, 'author': 'Lukman', 'author_id': 34586, 'author_profile': 'https://Stackoverflow.com/users/34586', 'pm_score': 2, 'selected': False, 'text': '<p>I wonder if a CAPTCHA mechanism that uses collage made of pictures and asks human to type what he sees in the collage image will be much more crack-proof than the text and number image one. Imagine that the mechanism stitches pictures of cat, cup and car into a collage image and expects human visitor to tick (checkboxes) cat, cup, and car. How long do you think will hackers and crackers will come up with an algorithm to crack the mechanism (i.e. extract image elements from the collage and recognize the object depicted by each picture) ...</p>\n'}, {'answer_id': 289430, 'author': 'Aaron Powell', 'author_id': 11388, 'author_profile': 'https://Stackoverflow.com/users/11388', 'pm_score': 2, 'selected': False, 'text': '<p>If you wanted you could try out the Microsoft Research project Asirra: <a href="http://research.microsoft.com/asirra/" rel="nofollow noreferrer">http://research.microsoft.com/asirra/</a></p>\n'}, {'answer_id': 523367, 'author': 'Eli Bendersky', 'author_id': 8206, 'author_profile': 'https://Stackoverflow.com/users/8206', 'pm_score': 2, 'selected': False, 'text': '<p>If you\'re just looking for a captcha to prevent spammers from bombing your blog, the best option is something simple but unique. For example, ask to write the word "Cat" into a box. The advantage of this is that no targeted captcha-breaker was developed for this solution, and your small blog isn\'t important enough for someone to actually develop one. I\'ve used such a captcha on my blog with some success for a couple of years now.</p>\n'}, {'answer_id': 21287682, 'author': 'Haje', 'author_id': 954987, 'author_profile': 'https://Stackoverflow.com/users/954987', 'pm_score': 0, 'selected': False, 'text': '<p>Just.. don\'t.. There are several reasons use of captcha is not advised.</p>\n\n<p><a href="http://www.interfacegeek.com/dont-ever-use-captchas/" rel="nofollow">http://www.interfacegeek.com/dont-ever-use-captchas/</a></p>\n'}, {'answer_id': 22096917, 'author': 'Toorion', 'author_id': 3360785, 'author_profile': 'https://Stackoverflow.com/users/3360785', 'pm_score': 0, 'selected': False, 'text': '<p>I use <a href="http://uniqpin.com" rel="nofollow">uniqpin.com</a> - it\'s easy to use and not annoying for users. So, bots can recognise a text, but can\'t recognize a image.</p>\n'}, {'answer_id': 24972264, 'author': 'user3879851', 'author_id': 3879851, 'author_profile': 'https://Stackoverflow.com/users/3879851', 'pm_score': 0, 'selected': False, 'text': '<p><strong>Death by Captcha can solve any Regular CAPTCHA (incude reCAPTCHA), but not Speedcoin Cryptocurrency Captcha.</strong> </p>\n\n<p>Death by Captcha - <a href="http://deathbycaptcha.com" rel="nofollow">http://deathbycaptcha.com</a></p>\n\n<p>Speedcoin Captcha - <a href="http://speedcoin.co/info/captcha/Speedcoin_Captcha.html" rel="nofollow">http://speedcoin.co/info/captcha/Speedcoin_Captcha.html</a></p>\n'}, {'answer_id': 24972337, 'author': 'ZeroBased_IX', 'author_id': 1888402, 'author_profile': 'https://Stackoverflow.com/users/1888402', 'pm_score': 2, 'selected': False, 'text': '<p>CAPTCHAS, I believe should start being considered heavily when designing the UX. They\'re slow, cumbersome, and a very poor user experience. They are useful, don\'t get me wrong but perhaps you should look into designing a honeypot.</p>\n\n<p>A honeypot is created by adding a hiddenfield at the bottom of the form. Because spam bots will fill in all the fields on the page blindly you can do a check:</p>\n\n<pre><code>If honeypotfield &lt;&gt; Empty Then\n   "No Spam TY"\nElse \n    //Proceed with the form \nEnd If\n</code></pre>\n\n<p>This works until there is a specifically designed spambot for your site, so they can choose to fill out selected input fields. </p>\n\n<p>For more information: <a href="http://haacked.com/archive/2007/09/11/honeypot-captcha.aspx/" rel="nofollow">http://haacked.com/archive/2007/09/11/honeypot-captcha.aspx/</a></p>\n'}]
['https://Stackoverflow.com/questions/59560', 'https://Stackoverflow.com', 'https://Stackoverflow.com/users/5287/']