One of the funner elements in the new version of Star Tours, is that someone on the ride with you (or you yourself) gets pulled into the story, by being identified as a Rebel Spy.
As to which guest gets their face projected for all others to see, it is not quite a random process. A cast member operating the ride is the one who chooses which guest will be featured as the Rebel Spy.
On one occasion, I saw a guest cheerfully joking and engaging with the Cast Member getting everyone lined up and loaded. Sure enough, this fellow ended up being the Rebel Spy for that flight.
A short while later, I had the opportunity to do this myself. Albeit, it was a short time before the park was closing, I was wearing a "I'm celebrating my Birthday" buttons, and there were like only 7 other people on the ride with me, but don't knock it, it worked!