Dashcam Speed Overlay?

[wrecksauce_II]

So, I will be turning 16 in just a few months and I want to have a camera to record the road in the case of an accident. But I also want to be able to have my speed show up all nice and fancy in the corner so if I am ever pulled over for speeding, and I think I'm not, I will have evidence. I researched this a little bit and I found out I would need to use a video overlay unit? I also saw another way but it required a lot of editing with many different programs on a pc. Do they sell a camera that will hook up to the vehicle's speedometer or something and do it for me? I have seen plenty of videos where this has been done, there must be a way! Please help.

[CaptainSi]

Having a dash cam is a great idea, however I think you're ill informed if you think a speed overlay will get you out of a ticket. Remember, speedometers are subject to factors like how much air is in your tyres and road surface smoothness, so they aren't necessarily accurate (generally speedos show you are going faster than what you are). Likewise, speedometers in GPS systems are inaccurate as they don't account for elevation changes, swerving, etc, and will generally show that you are going slower than you truly are. Just drive safely and with common sense and you'll be fine.