  Text CAPTCHA has been an effective means to protect online systems from spams
and abuses caused by automatic scripts which pretend to be human beings.
However, nearly all the Text CAPTCHA designs in nowadays are based on English
characters, which may not be the most user-friendly option for non-English
speakers. Therefore, under the background of globalization, there is an
increasing interest in designing local-language CAPTCHA, which is expected to
be more usable for native speakers. However, systematic studies on the
usability of localized CAPTCHAs are rare, and a general procedure for the
design of usable localized CAPTCHA is still unavailable. Here, we
comprehensively explored the design of CAPTCHAs based on Chinese characters
from a usability perspective: cognitive processes of solving alphanumeric and
Chinese CAPTCHAs are analyzed, followed by a usability comparison of those two
types of CAPTCHAs and the evaluation of intrinsic design factors of Chinese
CAPTCHAs. It was found that Chinese CAPTCHAs could be equally usable comparing
with alphanumeric ones. Meanwhile, guidelines for the design of usable Chinese
CAPTCHAs were also presented. Moreover, those design practices were also
summarized as a general procedure which is expected to be applicable for the
design of CAPTCHAs based on other languages.
