I'm sorry to hear about your injury, dog bites can be nasty wounds with large chance for infection if not treated (just slightly behind human bites ... no joke). You mention filing a police report, what did the police say? Is there an animal control services or similar in France? You have a picture of the dog, and there are other reports of attacks (e.g your friend and the driver's story), plus your injury, it seems enough to warrant some sort of visit from the appropriate authorities. I would follow up to ensure some sort of results. Good luck, and keep us updated!