Architectural design of a cloud-based reCAPTCHA service

reCAPTCHA is a security measure that guards web applications against automated abuse by presenting a random auto-generated challenge to users to solve. These challenges have to be devised to be hard to be solved by computers, yet easy for humans. In this paper, we present an architectural design for a cloud-based reCAPTCHA service and discuss key design issues. These issues include the extraction of individual word images from the scanned pages, optical character recognition (OCR) initial words classification, handling multiple users at the cloud-based service side, and usability and readability. We also show how our design addresses these issues at the implementation phase. It is worth noting that our reCAPTCHA service is designed for the Arabic language, but the underlying proposed architecture and design principles can be applied to any other language.