Projective homography sits at the heart of many problems in image registration. In addition to many methods for estimating the homography parameters , analytical expressions to assess the accuracy of the transformation parameters have been proposed . We show that these expressions provide less accurate bounds than those based on the earlier results of Weng et al. . The discrepancy becomes more critical in applications involving the integration of frame-to-frame homographies and their uncertainties, as in the reconstruction of terrain mosaics and the camera trajectory from flyover imagery. We demonstrate these issues through selected examples.