A proof-of-concept from the University of Maryland can defeat the audio challenges that are offered as an option for people with disabilities. Google has been working on refining and strengthening reCAPTCHA for years. It typically challenges users that it thinks might be bots by asking them to read distorted text and type it into a box, or to select groups of pictures that have something in common. The system downloads the audio challenge, breaks it into several digital audio clips, runs them through several text-to-speech systems to determine exact and near-homophones, weights the results by confidence level.
Source: https://threatpost.com/uncaptcha-googles-recaptchas/140593/