Capers are best known in their culinary role: the little pickled green things in a jar, so tasty on deviled eggs and often spotted in company with salmon, are the unripe buds of the caper bush. People also pickle and eat the ripe berry, and sometimes the leaves.
What are the white spots on capers? Well–okay, in the above photo, there are obviously large grains of salt. But even unsalted capers often show small white speckles. Those are crystallized spots of rutin, a compound formed as mustard oil is released from the pickled buds.