Pity the cop hassled you. You know why he was thinking about the Droit à l'image law (it occurs to me)? Because the police (the RG, the political police), break that law at every demonstration by secretly photographing everyone they can (obviously without their permission, which no one would give them since they wouldn't want their picture to end up in a police file). But you'll notice that on TV or in the press, you can see demonstrators quite clearly, which shows that the media flout the law (they don't have people's permission to use their "image" either).