Sequenced Tagged Captcha: Generation and its Analysis

Security of websites and online systems is of paramount concern today. A significant threat comes from malicious automated programs designed to take advantage of online facilities, resulting in wastage of resources and breach of web security. To counter them, CAPTCHAS are employed as a means of differentiating these bots from humans. However, highly sophisticated computer programs evolved over time have kept pace with all the current CAPTCHA generation schemes to render them ineffective. Due to the vulnerability of current CAPTCHAS, generation schemes of greater stability are required. Therefore, in this paper we propose a novel scheme of embedding numbers in text CAPTCHAS. It incorporates two levels of testing that includes identification of displayed characters and secondly interpreting the logical ordering based on the embedded numbers. Our CAPTCHA can be conveniently implemented on Web sites and provides the advantages of robustness and low space requirements. Discussion and conclusion, at the end of the paper, justify our approach.