On: Pluto image revealed by Nasa offers closest look yet at dwarf planet

[politician]

Can someone explain why we don't see any background stars in those photos?

[prewett → politician]

Pluto is a lot brighter than the stars at that distance, so they are underexposed (to the point of invisibility). If you look at pictures when New Horizons was farther away and Pluto therefor a lot dimmer, you'll see plenty of stars.