An active optical machine-readable tag (i.e. optical tag) is provided that is addressable and readable within a line-of-sight of a reader device, such as a mobile device equipped with a camera, at substantially large distances. A method and a system are provided for an active optical tag and a camera-based reader thereof that facilitate asynchronous communication at data rates that are sufficiently high for practical uses, while reducing the flicker associated with the low-frequency optical carrier to a level hardly noticeable by people. The optical tag may be formed as an array of light emitting elements, arranged in a single dimension (linear) or two dimension (planar) arrangement. The array may be embodied as part of a large display unit.