My new rescue, Merlin, does this. He barks at the oven (it's black) and the sliding glass door at night. I don't think he's used to clean glass or shiny ovens! I've tried explaining the whole reflection thing but he just doesn't get it.

I go with the distraction method and he loses interest pretty fast.
My dresser (mirror) is across the room at the end of my bed. Sometimes he'll catch his reflection in this but it's far enough way that he's not entirely sure what to make of it. Yet.
One of my other poodles, Pippin, loves to bark at the television. He seems to have really good vision because even if the thing is on mute and a dog/werewolf comes onscreen, he charges the TV. I tried explaining fantasy creatures to him to no avail. (He gets really agitated with those Wargs from LoTR!)