Around two years ago, Casey Henry of SEOmoz published an article about the effect CAPTCHAs have on conversion rates.
The article checked how many of the comments in a website are actually spam when there’s no CAPTCHA on that website. Then it checked how much spam there is and how many conversions are failed when the [...]

We have shown in this post some funny, weird and unsolvable Captchas. We know people understand the importance of spam prevention, but still dislike annoying form of Captchas. So if you could cast your vote, what would you choose? A text Captcha, sometimes a very hard to solve one, or something else, like AdsCaptcha’s Slider [...]

While there’s no room for doubt regarding the importance of CAPTCHAs for webmasters and blog owners nowadays, there are some complaints about how hard they become, sometimes impossible. Meaningless words or deformed letters that mash together to create… who knows?
 
Text CAPTCHAs are sometimes unsolvable, annoying or just a pain in the, well, eye. When all [...]

Image based Captcha is the latest alternative to current text based Captcha. It’s based on a set of images easier to be recognized and classified by human users than traditional textual Captcha. The user has to identify and click on a sequence of images. After he completes correctly the test and is verified as a human – he is allowed to carry on his online session.