Time to dust one off.

You don't seem to understand how cameras work, they set the exposure low so they can see the detail of the surface of the planet, but it's too low pick up stars because they are too faint. If the exposure was set to pick up stars, pluto would look like a big white splotch, which would negate the whole reason for going. It's the same reason why stars don't appear in the Lunar landing photos, or any photo of our planet.