it comes down to...they used a photo with your copyright mark on it..and even if you didnt stash that little type on the bottom of the photo, its still yours and they cant use it without your permission.
they cant argue that you didnt have permission to take photos of them b/c they came to a car meet to show off their car...someone taking photos of it, is a normal expectation of a car meet
, pretty much implied consent unless they had put a sign around it that said "no photos"