Although my images have been reduced (dark, bias, flats) and look good, vphoto refuses to recognize this and keeps giving me a red mark for calibration. The reduction information is in the fits header of the images I upload. Is there something I am missing, or is vphoto just picky?
There are many ways to write calibration information to the header, VPHOT understands only a few of them. Thus the red mark. But this information is not used for anything else than the marker, neither during analysis nor in reports, it is displayed to alert the user of missing calibration in images from remote telescopes (AAVSONet, iTelescope or similar). If you already KNOW that the calibration is ok, then no worries!
CALSTAT=BDF is one keyword option that works. I use CCDAP and Maxim DL which insert this keyword. As Geir noted, it is not required except to remind you that you did the calibration.