Analysis of tagging variants of Sequenced Tagged Captcha (STC)
Aditya Raj, Ashish Kumar Jain, Tushar Pahwa, Abhimanyu Jain · 2009
CAPTCHAs, a form of Human Interactive Proof (HIP), are means of enforcing security on web systems. The resources of these web systems are misused by automated `bot' programs which indulge in spamming and other unscrupulous activities. The objective of a CAPTCHA is to successfully identify and allow access to human users as against to these bots. To defeat all currently known CAPTCHA breaking techniques, the STC scheme was proposed. In this paper, we expand the STC scheme by identifying its variants based on the nature of `Tagging'. These variations occur in Tagging of characters and/or numbers in the CAPTCHA image. An in-depth analysis based on Readability and Security of the variant schemes is performed and concluded with a comparative result.