US Patent 9225531 Automated test to tell computers and humans apart

Techniques for verifying a user is human as opposed to a machine are provided. A series of images may be presented to the user sequentially along with a challenge question that instructs the user to select the image that is responsive to the challenge question. If the user selects the correct image, there likelihood that the user is a human as opposed to a machine is greatly increased. Techniques for varying certain parameters associated with display of images and challenge question are also provided. The variations in these parameters may further help distinguish human users from machines.