A new federal law, signed by the president on Tuesday, compels the Federal Aviation Administration to allow drones to be used for all sorts of commercial endeavors — from selling real estate and dusting crops, to monitoring oil spills and wildlife, even shooting Hollywood films. Local police and emergency services will also be freer to send up their own drones. But while businesses, and drone manufacturers especially, are celebrating the opening of the skies to these unmanned aerial vehicles, the law raises new worries about how much detail the drones will capture about lives down below — and what will be done with that information. Safety concerns like midair collisions and property damage on the ground are also an issue.