Captchas on Darknet Marketplaces: Overview and Automated Solvers

Captchas are used on many websites in the Internet to prevent automated web requests. Likewise, marketplaces in the darknet commonly use captchas to secure themselves against DDoS attacks and automated web scrapers. This complicates research and investigations regarding the content and activity of darknet marketplaces. In this work we focus on the darknet and provide an overview about the variety of captchas found in darknet marketplaces. We propose a workflow and recommendations for building automated captcha solvers and present solvers based on machine learning models for 5 different captcha types we found. With our solvers we were able to achieve accuracies between 65% and 99% which significantly improved our ability to collect data from the corresponding marketplaces with automated web scrapers.