Attacking Animated CAPTCHAs via Character Extraction

摘要

It is widely accepted that one of the principles in state-of-the-art text-based CAPTCHA design, requires that a robust CAPTCHA scheme be segmentation-resistant. This paper establishes the fact that the segmentation-resistant principle does not only apply to traditional single image CAPTCHAs, but is very much relevant to the design of animated CAPTCHAs. In this paper, we show that animated CAPTCHAs not designed with this principle in mind can be easily be broken using simple techniques to extract individual characters from the animation frames. We present our experimental results on attacking 13 existing animated CAPTCHAs.