Table 3 Typical audio-based CAPTCHAs
From: Human-artificial intelligence approaches for secure analysis in CAPTCHA codes
CAPTCHA | Challenge | Feature |
|---|---|---|
Google Audio reCAPTCHA | - Version 2008: Recognize eight spoken digits against a background of human voices speaking backwards at varying volumes - Version 2013: Identify all of the digits in the challenge that are divided into three clusters, each of which contains three or four overlapping digits - Version 2017: Recognize ten spoken digits in the presence of background noise | Background, noise, cluster, overlap |
eBay Audio CAPTCHA | Recognize six digits spoken in various voices with background noise | Six digits, background, noise |
Yahoo Audio CAPTCHA | Recognize seven digits that appear after three beeps made by a child against a background of other children’s voices | Seven digits, background, noise |
Microsoft Audio CAPTCHA | Recognize ten digits spoken in different voices over a regular background noise of several concurrent conversations | Ten digits, different voices, background |