CAPTCHA instances may be solved automatically by leveraging weaknesses in the creation process or by

A CAPTCHA image is designed so that a human can read it without difficulty while a computer is unable to.CAPTCHAs, which often appear as bitmaps of text characters, in order to gain access to a low-cost resource such as webmail or a blog. CAPTCHAs are generated by software and the structure of a CAPTCHA gives hints to its implementation. Thus due to these properties of image processing and image composition, the process that creates CAPTCHAs can often be reverse engineered. Once the implementation strategy of a family of CAPTCHAs has been reverse engineered the CAPTCHA instances may be solved automatically by leveraging weaknesses in the creation process or by comparing a CAPTCHA’s output against itself. we had try to implement the breaking of captchas using vector comparison algorithm.