imwty2 uses the Tycho-2 Catalog, an updated version of the Hipparcos Tycho Catalog containing two-and-a-half times as many stars, 2,539,913, with positions and proper motions. The 2MASS Point Source Catalog (imwtmc), with 155,569,249 stars, and the GSC II Catalog (imwgsc2), with 455,851,237 stars, are recent epoch catalogs without proper motions, if you need more stars. The USNO-A2.0 catalog (imwua2) also has a lot of stars (526,280,881), but is based on plates taken in the 1950's, so its accuracy has been decreased by proper motion of its stars.
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|