That's how ICE wants you to think about it, but they've tricked you. The rule that they actually implemented is that you must accept temporary detention while being scanned. If a random guy wants to take a picture of my face, he has every right to, but I in turn have every right to hide my face or flip him off and leave the scene before he gets a good shot. If ICE stops your car, and they don't trust your word that you're a citizen (or if you refuse to engage with them as is your right as a citizen), they will not let you leave until you've accepted a scan.