We propose and evaluate several novel types of CAPTCHAs (test to tell computers and humans apart) that exploit characteristics of the human visual system. Perceptions caused by the effect of lightness constancy or grouping phenomena due to transparent motion are hard to emulate on computers and may thus provide novel authentication mechanisms.

CAPTCHAs are the Internet’s first line of defense against automated account creation and service abuse. Google’s reCaptcha, one of the most popular captcha systems, is currently used by hundreds of thousands of websites to protect against automated attackers by testing whether a user is truly human. This paper presents unCaptcha, an automated system that can solve reCaptcha’s most difficult aud...

This study focuses on the human ability to tolerate subtle differences in color and categorize similar colors into a single mass enhance completely automated public turing test tell computers humans apart (CAPTCHA). First, an experiment was conducted check whether selection condition could control categorization results. Consequently, it clarified that when added, be categorized changed, implyi...

Completely automated public turing test to tell computers and humans apart (CAPTCHA) is widely used prevent malicious attacks on various online services. Text- image-CAPTCHAs have shown broader acceptability due usability security factors. However, recent progress in deep learning implies that text-CAPTCHAs can easily be exposed fraudulent attacks. Thus, are getting research attention enhance s...