  Spatial intensity moments computed on images can be used as a probe of the
centroid, size, and orientation of pixelized sources such as stars and
galaxies. However, all measurements made on images suffer from errors due to
undersampling and finite pixel size, causing systematic biases in the
computation of moments and other statistics. We show examples of bias in the
first and second geometric moments computed on images of Gaussian sources with
widths near the pixel scale, $0.1<\sigma<5$ pixels. We then illustrate how
undersampling could lead to the orientation angle patterns seen in various
modern surveys of the sky.
