Fiducial marker systems are systems of unique patterns and computer vision algorithms that help solve the correspondence problem, automatically finding features in different camera images that belong to the same object point in the world. Fiducial marker systems consist of patterns that are mounted in the environment and automatically detected in digital images using an accompanying detection algorithm, useful for augmented reality (AR), robot navigation, 3D modeling, and other applications. This paper compares the two recently developed systems ARTag and ARToolkit Plus on their reliability, detection rates, and immunity to lighting and occlusion. Processing in fiducial systems are defined as two stages, unique feature detection and verification/identification. The systems are compared considering these stages, experimental results are shown.