1. A device comprising: an input for receiving images captured by a camera, of an environment illuminated by light from a visible light source; an image processing module configured to process one or more of the images to decode a timestamp modulated into said light, and to output an indication of the decoded timestamp; and a verification module arranged to receive the indication of the decoded timestamp output by the image processing module, and based thereon to perform an at least partially automated verification of a time at which the one or more images were captured by comparing the timestamp as currently decoded from said image with a previously determined version of the timestamp; wherein the image processing module is further configured to apply a facial recognition and/or other image recognition algorithm to at least one of the captured images, and to thereby identify a person or persons appearing in the at least one image.