Fiducial images are a common method for supporting vision-based tracking in augmented reality systems. This paper addresses the question: what is the best fiducial? A set of criteria that are desirable in an optically tracked fiducial are presented and a new fiducial image set is designed that meets these criteria. The images in this set utilize a square black-border pattern with a 15% border width and an interior image that supports orientation determination and unique identification. The interior image is constructed from orthogonal DCT basis images chosen to minimize the probability of misidentification and to be robust to noise and occlusion. We describe how this image can be integrated into an AR software system such as ARToolKit.