19. The non-transitory computer storage of claim 17 , wherein the visual CAPTCHA is configured to update after an elapsed time, and wherein a prompt is provided to the human user to manipulate the at least one of the visual patterns after the elapsed time.
17. Non-transitory computer storage comprising instructions for causing one or more computing devices to validate visual CAPTCHAs by: generating a visual CAPTCHA including a plurality of visual patterns in a first configuration, wherein at least one of the visual patterns is configured to be manipulated by a human user to cause various amounts of overlapping of the visual patterns in order to produce different secondary images that are not visible in separate visual patterns of the plurality of visual patterns; providing to the human user an indication of a target visual pattern to be created in a produced secondary image of the visual CAPTCHA; receiving input from the human user indicating a second overlapping configuration of the visual patterns that produces a moire pattern, wherein the moire pattern is configured to be perceived as including a first object by the human user viewing the moire pattern, and wherein an automated computer system analyzing the moire pattern cannot identify the first object; comparing the second overlapping configuration to a predetermined target overlapping configuration associated with the target visual pattern; generating an indication of whether the second configuration was provided by a human based on said comparison; and transmitting the generated indication.