I suspect the answer is, "Ask a lawyer", but I'll ask here anyway...
If I take a picture of say a sculpture that's on public display in a garden, to which I've paid to enter, then as I took the photo, I own the copyright of that image correct? So far so simple?
If though I wanted then to make my photo into a greeting card and sell those cards, would I have first have to get permission of the artist that created the sculpture?