Facebook says it is banning “deepfake” videos, the false but realistic clips created with artificial intelligence and sophisticated tools, as it steps up efforts to fight online manipulation. Facebook said that it’s beefing up its policies for removing videos edited or synthesized in ways that aren’t apparent to the average person, and which could dupe someone into thinking the video’s subject said something he or she didn’t actually say. Created by artificial intelligence or machine learning, deepfakes combine or replace content to create images that can be almost impossible to tell are not authentic.