  We present a generic algorithm for performing astronomical image registration
and pointing refinement. The method is based on matching the positions and
fluxes of available point sources in image overlap regions. This information is
used to compute a set of image offset corrections by globally minimizing a
weighted sum of all matched point-source positional differences in a
pre-specified reference image frame. A fast linear sparse matrix solver is used
for the minimization. From these corrections, the pointings and orientations of
images can be refined in either a relative sense where pointings become fixed
(registered) relative to a single input image, or, in an absolute sense (in the
ICRS) if absolute point source information is known. The latter provides
absolute pointing refinement to an accuracy depending on the robustness of
point source extractions, match statistics, and accuracy of the astrometric
catalog used. The software is currently used in the Spitzer image processing
pipelines, although it is adaptable to any astronomical imaging system which
uses the FITS image format and WCS pointing standard. We test the algorithm
using Monte Carlo simulations and compare them to image data acquired with the
Infrared Array Camera (IRAC) on board the Spitzer Space Telescope.
