Are CAPTCHAs preventing robotic intrusion or accessibility for impaired users?

Is the World Wide Web for everyone? Long story short: no and unfortunately it is not only a matter of infrastructures, level of instruction or economic conditions. People affected by visual impairments have often difficulties in navigating web pages for a wide range of reasons. One of the biggest obstacles nowadays is the use of CAPTCHAs, powerful tools against bot attacks but also potential virtual barriers for the aforementioned category of users. In this paper we tested various categories of CAPTCHAs with people affected by visual impairment and not, to understand how discriminatory can be these cybersecurity measures.