The basic premise of string theory is that everything is made up of vibrating filaments and membranes made out of energy. In other words, strings and... well... branes. String theory is a newer theory that attempts to explain things like gravity using quantum physics. The answer I gave about black and white holes earlier is part of string theory.
The thing is, string theory is kind of heady. Part of string theory includes parallel universes, several extra dimensions, and all sorts of things that sound like something from the sci-fi channel after midnight. That's the part of it that I'm kind of .-. about.
The real question is "where is space black". When you are on Earth, space actually appears to be Navy Blue (a really dark shade of it). In space, however, we see black everywhere. The majority of it seems black to us. Now, the thing is, it's not black. It's simply not reflecting light. Imagine a white room with no light source. It appears black, but isn't really black. So the answer to your question is that space isn't black, it's just dark.
This actually depends on the photographer. In quite a few photos of the individual planets, photographers actually cut out a good chunk of the background to allow you to focus on the planet. Or they recreate the planet using modelling based on photos rather than taking an actual photo. These tend to be the most popular "photos" of the planets.
As for why the background isn't as clear in the other photos but is still there, it's because of the giant planet taking up the point of focus that makes it seem as if there isn't much else in the photo.
The thing about the things in space that might kill us eventually is that by the time they do eventually become a threat we will have learned how to avoid their threats. As for war, that's actually the current most likely thing to end our species' reign on this planet.
That being said, we are survivors. That's what humanity is good at. Think about it. We are not suited for living outside like the other animals, without tools we would have trouble hunting, and we require the protein in most meats to survive. If we did not have intelligence, then we would have a tougher time of things than most animals would. Since we got our intelligence, we've started living nearly everywhere on the planet and surviving it. We even live in the parts of Antarctica that nothing else can. Here in another 10 years, we'll even live on Mars (if things go well).
So, if ANYTHING is going to kill us, it will be either ourselves or the heat-death of the universe.