In (Cyber)Space Bots Can Hear You Speak
Saumya Solanki, Gautam Krishnan, Varshini Sampath, Jason Polakis · 2017
Captchas have become almost ubiquitous as they are commonly deployed by websites as part of their defenses against fraudsters. However visual captchas pose a considerable obstacle to certain groups of users, such as the visually impaired, and that has necessitated the inclusion of more accessible captcha schemes. As a result, many captcha services also offer audio challenges as an alternative.