How are you adding the photo to your file? As media added to fact, or a source, or to the person themselves?
Most people will add the photo as part of a source citation. I don't often enter as individual headstones (usually from a listing), but, if I did, it would be something like:
Create a Burial Fact for, say Bill Smith, and I would then add the cemetery address in the fact place field: Country Club Cemetery, Hoboken, Kansas, USA
In the source citation, I would enter:
Citation Detail: Personally observed 02/07/2013
Citation Text: Photo of joint stone: "Bill (1900-1980) and Mary (1910-1980) Smith" or "Photo of partially readable joint stone..." or ""Photo of joint stone: Bill (1900-1980 and Mary (1910-198? (year not readable)) Smith"
I would then add the photo as Media to the citation, click ok.
I would then select the citation and copy it (via the button bar copy icon).
I would then add another Burial Fact for Mary, and add the cemetery name and address to the Place field and then Paste-Link the citation to the second Burial Fact. (or choose the fact and right click Copy, then Right-click paste - then select Mary - that copies and pastes the fact together with the citation all at once from husband to wife)
You can then add the citation to the Name, birth, and death fields, as well, again by Paste-link the citation from the button bar.
You could enter the inscription in the Description field of the Burial Fact, or the Fact Note for the Burial Fact, rather than the Citation Text field of the Citation - depending on whether you want to print the inscription in the body of a report or in a long list of endnotes.
If you have directions to the cemetery or to the headstone within the cemetery, or other misc notes, or an exact GPS for the headstone, etc, you could enter those in a Fact Description or Fact Note.