I notice a mistake in an article and want to comment on it to notify the author about the mistake. Domain-specific CAPTCHAs can be hugely annoying when actual users have no idea about the answer.Example: I'm visiting a page on a movies-oriented website.I tried to find some material about how effective those are, but without success, so here is just my personal opinion: You may want to move from visual CAPTCHA to sound (if you're not using both already, and you should), but this means that users with hearing impairment would be unable to use your application.įrustratedWithFormsDesigner and GalacticCowboy mentioned in the comments domain-specific CAPTCHAs. Technically, nothing would prevent human farms: you may create animated GIFs where several frames display different text very quickly and only one frame is actually visible by the user, you may distort or bend text in all directions, or you may find alternative ways to prevent OCRs from recognizing text, but humans paid for solving CAPTCHAs will still successfully solve them. If you use a popular CAPTCHA mechanism, moving to a custom-made one or to another popular one might prevent OCR.
This will help if either your own CAPTCHA was too easy to OCR, or if there was a bug which was successfully exploited. If you have your custom implemented CAPTCHA, you may try to move to a popular one, like reCAPTCHA.One of the first documented attacks on the system was by a Carnegie Mellon student, who associated CAPTCHA images with access to an adult Web site, thus gaining free human labor to crack the authentication.Įxternal projects have shown methodologies and results indicating that many of the systems can be defeated by computers with between 88% and 100% accuracy, using optical character recognition. There may also be a bug either in the CAPTCHA mechanism itself or the surrounding application, allowing someone to bypass the CAPTCHA.īy the way, the W3C article Inaccessibility of CAPTCHA : Alternatives to Visual Turing Tests on the Web explains as well how CAPTCHAs could be compromised: ask for people to fill CAPTCHAs for money, just like ProTypers does. Two of the easiest ways to get through CAPTCHA: How can I prevent this? Should I change to another type of CAPTCHA? Why? How do robots beat the CAPTCHA? Do they use some kind of advanced OCR or just get the solution from where it is stored? I use a custom CAPTCHA to prevent spam from robots. This Q&A is part of a weekly series of posts highlighting common questions encountered by technophiles and answered by users at Stack Exchange, a free, community-powered network of 100+ Q&A sites.
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