During the first 15 minutes of the film, during the rebel leader speech, you can see the back of one of the computers with no wires attached (power, keyboard, monitor cables...etc)
In the last few minutes of the film, a man wearing a white and red, "Where's Wally", shirt in the crowd shot appears multiple times, making it clear that the shot is actually a multiple composite shot of about ten or so extras standing in a diamond shape waving their arms around.