On the invariance of differential scale invariants

Many geometric invariants have been reported in the literature. For two specific differential scale invariants we discuss the parameters involved and analyze the accuracy of their computation on real camera data. Our experimental data show significant errors in the observed values. Those errors seem to be inherent in the image formation and scaling process. They indicate the limitations of local differential computations and, more generally, the problems of synthetically scaled images as models for zoomed images.