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FIGURE 14.1
reCAPTCHA: (A) The original reCAPTCHA asked users to type in words that could
not be recognized via optical-character recognition. A sample of text that might have
been recognized is shown, along with a depiction of how the text might be distorted
before being presented to the user. (B) More recent reCAPTCHA tasks involve image
classification, such as choosing images from a set that match a specified criteria—in
this case, images containing fireworks.
(A) From von Ahn, L., Maurer, B., McMillen, C., Abraham, D., Blum, M., 2008. ReCAPTCHA: humanbased
character recognition via web security measures. Science 321, 1465–1468;
(B) From https://www.google.com/recaptcha/api2/demo (accessed April 8, 2017).

(Continued)