“IF ONLY I’D HAD A VIDEO,” you might’ve thought at one point, “I could prove that that scumbag ran the two-way stop,” or “I could prove he rolled backward” or any of the other stupid things people do. You’ve been on YouTube, so you know that everybody in Russia—and, to a lesser extent, in other European countries—has a dash-mounted camera. They’re catching on here. In 2017, Americans bought 237,000 of them, and sales are projected to rise to 285,000 units by year’s end, says Danielle Cassagnol, a spokesperson for the Consumer Technology Association. Why, then, do auto-insurance companies still not offer a discount for using one, have no standard policy on accepting or reviewing footage, and refuse to nudge you to get one when they practically beg for post-accident photographs?…