View a 2-frame ds9 to view two different images of the same field and mark corresponding sets of objects. This is very much like ds9_2f, except a catalog of stars (STARS.cdfp) is used to overplot star positions on the DSS image frame (#2 on the right side of the ds9 gui).

ds9_2f_with_cat a.fits STARS.cdfp.reg

arg1 - image #1 
arg2 - image #2  (usually the DSS image) 
arg3 - regions file for the CDFP input catalog