The 1964 Supreme Court Case Jacobellis v. Ohio presented a highly subjective question to the justices: what is obscenity or pornography? How do you define it? Where do you draw the line? In response, Justice Potter Stewart gave us the iconic line, "I know it when I see it."

His ambiguous answer works fine for humans who can make judgement calls on the fly, but the algorithms that rule our lives need rules that are much more concrete. Say you flag something as inappropriate on social media. How is artificial intelligence meant to answer a question that even the Supreme Court could not definitively pin down?

That’s where humans come in. Mary Gray, an anthropologist and co-author of the book,“Ghost Work: How to Stop Silicon Valley From Building a New Global Underclass,” explores the work and lives of the real people behind online processes that internet users may assume are purely algorithmic. From analyzing medical tests, to flagging questionable social media posts, to identifying your rideshare driver, Gray argues that the human touch of “ghost work” is not only essential, but this hidden workforce will continue to keep growing.