CAPTCHA generation as a web service

Abstract

We present an implementation of CAPTCHA image generation as a REST-style web service, currently available at http://captehaservice.org. We argue that CAPTCHA generation is well suited to a web services approach, particularly one powered by open-source code, and discuss techniques for using such a service to protect weblogs from comment spam attacks. We describe the captchservice.org API by example, and detail the workings of the two image-distortion techniques that the service offers. We also discuss accessibility objections to visual CAPTCHAs, describe our early attempts at non-visual alternatives, and summarize future development directions. © Springer-Verlag Berlin Heidelberg 2005.