The role of visual features in text-based captchas: an fnirs study for usable security

Mülazimoğlu, Emr
In order to mitigate dictionary attacks or similar undesirable automated attacks to information systems, developers mostly prefer using CAPTCHA challenges as Human Interactive Proofs (HIPs) to distinguish between human users and scripts. An appropriate use of CAPTCHA requires a setup balance between robustness and usability during the design of a challenge. The previous research reveals that most of the usability studies have used accuracy and response time as measurement criteria for quantitative analysis. The present study aims at applying optical neuroimaging techniques for the analysis of CAPTCHA design. In particular, fNIRS (Functional Near Infrared Spectroscopy) is a neuroimaging technique used for mental workload analysis by means of analyzing hemodynamic responses on brain. The present study reports an experimental investigation in which 25 participants solved a group of text-based CAPTCHA with various visual characteristics.