One of the primary criteria we hear from customers when selecting a dash cam is the camera's ability to pick up license plates and while that seems like a simple idea it's actually much more complicated in practice. There are two main limitations we want to discuss which apply to all dash cams
Vehicle Speed Differential - If your vehicle is travelling at a much faster or much slower speed than the other vehicle, chances are you aren't going to pick up the license plate. Most dash cams on the market shoot at 30 FPS and a speed differential greater than 10 mph would likely result in that license plate blurring simply due to physics. That being said if there was some point where you were travelling at more or less the same speed during your drive you might be able to get the license plate via that segment.
At a low speed differential even oncoming license plates can be picked up (captured on Skyview G1)
In this same clip, the higher speed differential makes the license plate illegible although the make and model of the vehicle is still clear
License Plate Material/Design - Many dash cam sample videos come from Europe and Asia where license plates have big bold letters and don't have a reflective white surface. In North America however, our plates often use very thin font that is not picked up as easily by video cameras. At night this effect is very clear when your own vehicle's headlights are reflecting off of the plates in front of you. This might not be very obvious to the naked eye but it in fact makes reading license plates very difficult for dash cams. There is no CPL filter that can truly remove this type of glare either.
Again the model and colour of the vehicle is apparent but the plates just appear as a bright white rectangle
With these limitations in mind, it's important to note the primary purpose of a dash cam is to prove who is at fault in an accident when you submit it to your insurance provider/law enforcement. Drivers should still be exchanging information if they get in an accident and should have time to note the license plates. If in the case an accident was recorded on the dash cam but the license plate not captured, that doesn't render the footage useless since the driver would have the plate and other contact info from the other party any way.