  The purpose of this paper is to introduce a set of four test images
containing features and structures that can facilitate effective examination
and comparison of image processing algorithms. More specifically, the images
are designed to more explicitly expose the characteristic properties of
algorithms for image compression, virtual resolution adjustment, and
enhancement. This set was developed at the Naval Research Laboratory (NRL) in
the late 1990s as a more rigorous alternative to Lena and other images that
have come into common use for purely ad hoc reasons with little or no rigorous
consideration of their suitability. The increasing number of test images
appearing in the literature not only makes it more difficult to compare results
from different papers, it also introduces the potential for cherry-picking to
influence results. The key contribution of this paper is the proposal to
establish {\em some} canonical set to ensure that published results can be
analyzed and compared in a rigorous way from one paper to another, and
consideration of the four NRL images is proposed for this purpose.
