4chan also exploited reCAPTCHA when it was just bought by google and they used it to OCR books. reCAPTCHA provides you with two words, and one is much easier to recognize than the other. So 4chan users created a simple website with lots of reCAPTCHAs, typed in the easy word correctly to pass the test and typed in &quot;nigger&quot; instead of the second word. As many users raided at the same time, Google OCRed hard to recognize words as &quot;nigger&quot;.<p>Edit: found related link
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