On the Viability of CAPTCHAs for use in Telephony Systems: A Usability Field Study

  • Niharika SachdevaEmail author
  • Nitesh Saxena
  • Ponnurangam Kumaraguru
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 7807)


Telephony systems are imperative for information exchange offering low cost services and reachability to millions of customers. They have not only benefited legitimate users but have also opened up a convenient communication medium for spammers. Voice spam is often encountered on telephony systems in various forms, such as by means of an automated telemarketing call asking to call a number to win a reward. A large percentage of voice spam is generated through automated system which introduces the classical challenge of distinguishing machines from humans on telephony systems. CAPTCHA is a conventional solution deployed on the web to address this problem. Audio-based CAPTCHAs have been proposed as a solution to curb voice spam. In this paper, we conducted a field study with 90 participants in order to answer two primary research questions: quantifying the amount of inconvenience telephony-based CAPTCHA may cause to users, and how various features of the CAPTCHA, such as duration and size, influence usability of telephony-based CAPTCHA. Our results suggest that currently proposed CAPTCHAs are far from usable, with very low solving accuracies, high solving times and poor overall user experience. We provide certain guidelines that may help improve existing CAPTCHAs for use in telephony systems.


Session Initiation Protocol Edit Distance Federal Trade Commission Voice Over Internet Protocol System Usability Scale 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



The research of the first author is supported by TCS (Tata Consultancy Service) Research Scholarship. We would like to thank Dr. Iulia Ion and Paridhi Jain for their input on the study. The authors would also like to thank International Development Research Centre (IRDC) and all members of PreCog research group at IIIT-Delhi. We would like to thank Siddhartha Asthana for helping in deployment of the system and all participants in the study.


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Copyright information

© Springer International Publishing Switzerland 2015

Authors and Affiliations

  • Niharika Sachdeva
    • 1
    Email author
  • Nitesh Saxena
    • 2
  • Ponnurangam Kumaraguru
    • 1
  1. 1.IIIT-DelhiNew DelhiIndia
  2. 2.University of Alabama at BirminghamBirminghamUSA

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