Spam-Protect web forms

Spam is not only a problem for emails, but more so for web forms. Bots from spammers try to fill out forms all over the internet. But unlike in your email inbox, the data from your web forms normally does not get spam filtered, which makes spam in these cases an even bigger problem. The goal is to add spam protection (CAPTCHA) to your web forms to make sure only humans fill in and submit the form.
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using reCAPTCHA

A CAPTCHA, short for "Completely Automated Public Turing Test To Tell Computers and Humans Apart" is a program that protects websites against bots by generating and grading tests that humans can pass but current computer programs cannot. Normally they use distorted text, which humans can readbut current computer programs and OCR software can't.

reCAPTCHA is a free service which can be integrated into a website via plugins for multiple programing languages (PHP, ASP.NET, Java, Perl, ...) and content management systems (WordPress, MediaWiki, ...)

Additionally to helping you handling your spam-problem, reCAPTCHA helps digitizing books by showing words that could not be deciphered by OCR software and letting them read and fill in by humans.