Limiting Camera Boundaries

How do you limit the camera boundaries to just a certain section of the map?

There's a clever little native specifically for it.
I prefer the BJ, though, as it takes a rect and does it for you without leaking.

Is it possible to change the minimap picture with it?

Changing the minimap picture at runtime is impossible unless you use custom mercenary camp/gold mine icons and make them the size of the minimap. Otherwise, no, it cannot be done. You can change the minimap at map initialization by importing a special blp/tga file, though, look at Tim's map for an example.

How do you do that? (Thread necromancy )

The easiest way i know is to use WEU.

You sure its not just import some tga/blp file of a certain size and changing the name to something? I just don't know the specifics.