1. A user device, comprising: a processor implementing an expression classifier; a display; a camera; and a network interface; wherein the processor of the user device is configured to execute code to evaluate an image captured by the camera for presence of a predetermined expression using the expression classifier, and to allow a user of the user device to view on the display the image captured by the camera, and to transmit over a network at least one of (1) the image captured by the camera, and (2) depersonalized data derived from the image, to a computer system in response to identification by the user of a discrepancy between output of the expression classifier corresponding to the image captured by the camera and appearance of the image captured by the camera.