[1] [CITE[reCAPTCHAの無茶振りとその理由 - しろもじメモランダム]]
([TIME[2012-05-21 15:26:32 +09:00]] 版)
<http://d.hatena.ne.jp/mashabow/20110930/1317400512>

[2] [CITE@en[Google Online Security Blog: Are you a robot? Introducing “No CAPTCHA reCAPTCHA”]]
([TIME[2015-01-22 02:46:51 +09:00]] 版)
<http://googleonlinesecurity.blogspot.jp/2014/12/are-you-robot-introducing-no-captcha.html>