A system and method for monitoring the state of an individual. The method includes providing a stimulus to the individual, measuring a response to the provided stimulus, comparing the measured response to an expected response, and diagnosing one or more aspects of disease in accordance with the result of the comparison between the measured response and the expected response. The stimulus may be a predetermined test sequence, such as a visually displayed predetermined sequence of images, or may include observation of the physical response of the individual while performing one or more predetermined activities. Stored images or video of the individual responding to one or more test sequences may be stored in a lossy or lossless state, and thus security and de-identification may be provided to stored data. This stored data may also be de-identified in a manner to allow for the answering of the greatest number of future questions.