ARTag is a 2D marker and computer vision system for Augmented Reality, a Fiducial marker system, that was introduced in a prior NRC publication . Augmented Reality (AR) is an emerging display paradigm, an enabling technology of AR is vision based pose tracking. Pose can be found accurately and with low cost using a camera as the only special hardware. Fiducial marker systems consist of patterns that are mounted in the environment and automatically detected in digital images using an accompanying detection algorithm. They are useful for AR, robot navigation, and general applications where the relative pose between a camera and object is required. ARTag is a marker system that uses digital coding theory to get a very low false positive and inter-marker confusion rate with a smaller required maker size, employing an edge linking method to give robust lighting and occlusion immunity. ARTag markers are bi-tonal planar patterns that consist of a square outline with a digital 36-bit word encoded in the interior. The digital word contains a unique ID number protected from false detection with the digital code techniques of checksums and forward error correction (FEC) providing very low and numerically quantifiable error rates. ARTag's performance is theoretically or experimentally examined for nice characteristics import to AR; false positive and false negative detection rates, inter-marker confusion probabilities, immunity to lighting, immunity to occlusion, minimal marker size, vertex jitter, marker library size, and speed performance. This publication further characterizes ARTag and provides more detailed information and experimental results useful for those interested in utilizing ARTag, and those interested in fiducial marker systems themselves.