A mysterious speckle

I woke up at about six thirty this morning and then decided to go outside the house. Unlike yesterday, the sky was clear and there it was, Jupiter hanging high up above me. I took out my camera and started shooting in multiple mode. Yes, this time, all four of the Galilean moons were visible when I digitally magnified the frames. But wait a minute. What was that very barely visible speckle of light that was moving up from the lower right corner of the pictures. Asteroid? Space junk? Dirt on my lens? Could be anything. The sequence below shows its migration.