Wind-shake, astigmatism, etc., can cause differences in image shape (e.g.
orthogonal elongation) which cannot be transformed to a common shape using
convolution. In these cases, our image subtraction software will detection
residual subtraction errors and flag these as candidate supernovae.

The task is to develop diagnostics, from the input images or the subtraction
image, so that these spurious candidates can be flagged. Since subtraction
errors are highly correlated, it would be best to define search exclusion
regions. These regions will have to be cataloged so that we know exactly
where we have searched.