A novel dynamic CAPTCHA based on inverted colors

CAPTCHA (also known as verification code) is mainly used to guarantee the login security of the interactive websites. At present, the most popular verification code is image CAPTCHA which can distinguish the human user from the computer by identifying characters in the image. Although the image CAPTCHA is safe at beginning, great deals of CAPTCHAs have been cracked by the computers along with the development of image processing technology and artificial intelligence technology. This paper presents a new dynamic CAPTCHA based on inverted color. The characters color and the background color in the CAPTCHA are inverted respectively, the interference lines are added in the foreground image and multi-frame dynamic images are compounded to ensure the CAPTCHA has better visual effects, and thus, it is easy for the human to identity the real information while hard to remove the interference information by normal image processing technology. Theoretical analysis and simulation experiments prove that the CAPTCHA is safe and efficient.