The tiny aircraft, which resembled hobby-shop model planes contained consumer-grade cameras, were found after they landed, immediately south of the border with North Korea, in March and April.
The plastic planes did not pose a threat to South Korean security, although they did traverse South Korean air defenses, and were found as tensions continue to rise over the expected detonation of a fourth North Korean nuclear device.
Analysts concluded that "all three were sent from North Korea and are programmed to return to North Korea," said South Korean defense spokesman Kim Min-soek, adding aerial photos the drones took corroborated their flight path.
The tiny planes were programmed to fly over military facilities, and one had overhead photos of the Blue House, the South Korean president's residence and office. They were not equipped to transmit photographs back to North Korea, and were stumbled upon by a civilian digging for wild ginseng.