Complexity Analysis of Image-Based CAPTCHA

In the field of information security, CAPTCHA technology is a recent successful achievement. Apart from using different text CAPTCHAs, image-based CAPTCHAs are also in existence. Though text based CAPTCHAs are in regular usage in internet services, the vulnerability in text CAPTCHAs has compiled us to move on to the image based CAPTCHAs. Therefore before implementing image based CAPTCHAs publicly, it is necessary to analyze the different complexity issues related to image based CAPTCHAs. In this paper we have presented the analyzed results based on the complexity issues including both space and time. The analysis is done on the data collected with the help of gamification of image based CAPTCHAs called CAPTCHINO.