1. Use HTML. I assume that's all you're asking, since the exact code is shown in the table to the right of the window I'm currently typing in, which you see anytime you make a new post. Replace "image.jpg" with the full URL to the image you are trying to display.
2. Most likely for gameplay and balance, so other vehicles which are capable of crossing those terrains aren't rendered entirely useless. I suspect that vehicles, like ships, will be reviewed once more prior to combat.