A Captcha Mechanism By Exchange Image Blocks

Abstract

The need to tell human and machines apart has surged due to abuse of automated `bots'. However, several textual-image-based CAPTCHAs have been defeated recently, calling for the development of new anti-automation schemes. In this paper, we propose a simple yet effective visual CAPTCHA test by exchanging the content of non-overlapping regions in an image. We give in-depth analysis regarding the choice of parameter and image database during the test generation phase. We also contemplate possible ways, including: 1) random guess, 2) collect and match, and 3) image segmentation, to defeat the proposed test and provide counter-measures when necessary. Preliminary experimental results have validated the efficacy of the proposed CAPTCHA, although we expect that a large-scale experiment to collect and analyze user responses contribute to optimal parameter settings