Mine cut diamonds actually have a cushion like outline, in addition to the large culet (facet at the bottom point) that looks like a dark spot, as has been mentioned. Round diamonds that have the high crown, deep pavilion, and large culet are called European cuts (regardless of where they were actually cut).
Generally, mine cuts were before 1900 and European cuts were 1900 to 1930ish. But it was a constant improvement and refinement of the cut. Early European cuts were close to mine cuts and late European cuts were close to modern round brilliant cuts. Round brilliants even through the early 1950s often even have a different look than later brilliants.
And yes...we can't tell from a photo. But...with a very good, enlarged photo, we could probably make a very good guess. The setting looks very 1960s, so it very well could be an older diamond that was reset into a "modern" setting then. Now we would call it "retro-modern".
