22:37:49.4 -08:39:03 1991.2 40.9
Where the first two fields are the RA and Dec, the next is the coordinate epoch (always the date of the image).
The program converts the coordinates using CTYPEn, CRPIXn, CRVALn, CDELTAn values that must be present for both axes in the header. It calculates the epoch of the observation from the DATE-OBS and UT keywords. These keywords are discussed briefly in the man page for photo. If any of these keywords are not found in the header the program exits with a nonzero code.
If you wish to precess to the coordinates to another equinox, the output can be piped to precess.
inverse - converts ra, dec, epoch lines to row/columns.