A new architecture for the generation of picture based CAPTCHA

Automated network attack such as denial-of-service (DoS) leads to significant wastage of resources, which is a common threat to network security. To prevent these automated network attacks CAPTCHA based security mechanism is to be adopted so that it will differentiate humans from machines. Optical Character Recognition (OCR) based CAPTCHAs are more vulnerable to automated attacks due to the existence of correlation algorithms and direct distortion estimation techniques. The illegibility of the text CAPTCHA makes the user difficult to read it and thus they feel uncomfortable. In order to overcome these difficulties a new type of CAPTCHA, that is, picture based CAPTCHAs came into existence, which are more efficient and secure than the existing text based CAPTCHAs. We propose a new architecture for the generation of picture based CAPTCHA, which is resistant to segmentation through edge detection and thresholding, shape matching and random guessing. Our security analysis shows that the proposed architecture is showing better results in comparison with other picture based CAPTCHAs.