The Evaluations of Deletion-Based Method and Mixing-Based Method for Audio CAPTCHAs

  • Takuya Nishimoto
  • Takayuki Watanabe
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 6179)


Audio CAPTCHA systems, which distinguish between software agents and human beings, are especially important for persons with visual disability. The popular approach is based on mixing-based methods (MBM), which use the mixed sounds of target speech and noises. We have proposed a deletion-based method (DBM) which uses the phonemic restoration effects. Our approach can control the difficulty of tasks simply by the masking ratio.

According to our design principle of CAPTCHA, the tasks should be designed so that the large difference of performance between the machines and human beings can be provided. In this paper, we show the experimental results that support the hypotheses as follows: (1) only using MBM, the degree of task difficulty can not be controlled easily, (2) using DBM, the degree of task difficulty and safeness of CAPTCHA system can be controlled easily.


Security Visual Impalement Speech Recognition  CAPTCHA Mixing-based Method Deletion-based Method 


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Copyright information

© Springer-Verlag Berlin Heidelberg 2010

Authors and Affiliations

  • Takuya Nishimoto
    • 1
  • Takayuki Watanabe
    • 2
  1. 1.Graduate School of Information Science and TechnologyThe University of TokyoTokyoJapan
  2. 2.Department of Communication, Division of Human Science, School of Arts and SciencesTokyo Woman’s Christian UniversityTokyoJapan

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