Ugh, this is awful, and it's NOT nothing.
Men rely on us doing nothing because we are conditioned not to make a fuss, not to cause a scene. In short (excuse the pun) we don't put ourselves first, and then we end up angry at ourselves in hindsight.
Just suppose he's done that to a dozen women? If every woman had even said "Hey, WTF?" people around would begin to get the picture. Perhaps the threat of him being known as a nasty voyeur would be enough to make him stop?
Not sure if he did that? Go up to him and ask him if he was just photographing or filming him. You know he really was, but just asking him tells him that you know what he did. Again, if more than one woman does this, it begins to build up a picture.
Women are not responsible for the behavior of men, nor are they responsible for preventing it. But, we owe it to ourselves to put our dignity and safety first and foremost when we're in a situation where the other person isn't doing either.
I'm so sorry this has happened to you.