I've seen one of these GoPro cameras in action. They're pretty cool but made really, really cheaply . The one I saw had troubles staying on because of a faulty switch. I had thought about getting one of those things at one point, but after seeing the issues the person had with the camera, I decided against it. After reading various review on them, I think I'll wait a bit longer. The reviews vary from awesome to less than favorable due to the inconsistent quality.
There are some cameras that can be mounted to railcars. I've seen those at the model train shows and the images are okay. In part I think is because the video was transmitted and the camera received power from the track. Every time the camera-train went over turnouts and lots of crossings, the image was a bit jumpy with lots of static. Given the technology we have today, I'm sure someone has already rigged up a better camera than those that I saw which writes to a small ssd-chip (jump drive/thumb-drive) instead of being broadcast through a UHF TV channel.
John