zoobie,
You did hit on something important. In copyright law, there’s something known as de minimis, which is basically along the lines of if you used a copyrighted work (and people are protected from their image being used through copyright) in an itty bitty way, it’s alright. A sea of people, shops in the distance, heck even a passing truck behind your talent (so long as it doesn’t stop) can be considered safe.
Still, as far as releases go, be safe and get what you can, when you can.
