That's very interesting. It's not moving with the background stars. However it could still be a camera artifact - see how there's a 'trail' behind Pluto's disc? In frames 4-7, the object you've identified is in the same position relative to the trail (off to the right if you are following a line outwards from Pluto along the trail).

I made an image to show what I mean. See frames 4-7; it's not an exact match but maybe it's a clue: http://i.imgur.com/TADflVd.jpg