imwgsc uses the Hubble Space Telescope Guide Star Catalog, which contains 25,541,952 entries, and works on about half of the 10 arcminute square images I've encountered. The GSC-ACT Catalog is a more accurate version of the same catalog, and can be invoked using imwgsca. The USNO-A2.0 catalog has enough stars to fit almost any ground-based image, and is invoked using imwua2. The 2MASS Point Source Catalog (imwtmc) and the GSC II Catalog (imwgsc2) have fewer stars than the USNO-A2.0, but they are based on positions closer to the present, i.e. 1990's rather than 1950's.
A set of image stars may be hand-matched to sky positions and used to get a WCS or set initial values for a reference catalog-based WCS (See example).
|Using SExtractor to find stars in an image|