Why is it hard to identify drones?

(NewsNation) — Drones have been spotted for more than a month in multiple states.
Although the number of sightings around the United States has dropped recently, and the FBI has dismissed many of the 5,000 reported as manned aircraft, the agency told reporters there are still more than 100 sightings that need to be investigated.
Concern grew after a large number of drones began flying over sensitive military sites in New Jersey in mid-November. White House and Pentagon officials have