Proposal and evaluation for color constancy CAPTCHA

摘要

CAPTCHAs are technologies that distinguish humans and bot to prevent illegal access. Unfortunately, current CAPTCHAs, even the latest Google reCAPTCHA, have already broken with high accuracy. Although the devices, including emphasizing the distortion of the text and adding noise to the image, improve the machine resistance, they may decrease the accessibility of the web page. The purpose of this study is to propose a new CAPTCHA that can decrease the machine resistance while keeping usability. To achieve this purpose, we focused on color constancy. Color constancy is a human's characteristic that enables humans to recognize the original color of the object by ignoring the effects of illumination light. Color constancy has not been fully reproduced by the program yet. We proposed color constancy CAPTCHA that the user is required to answer an original color of the object in a specified area on the CAPTCHA image with a color filter. In this paper, we created a prototype of CAPTCHA, applied two kinds of color filters, and then evaluated each case for the human success rate, machine success rate, and usability.