I've always heard that dogs can't see what's on television. That they can tell maybe there's some lights or some glowing from a TV set, but other than that, they can't actually make out what's on it.
But I think it's time to re-evaluate this in light of plasma screen TV's. The majority of my day is spent on my couch, with the TV on, and my dog at my side. And every single time there's another dog on the TV screen, my dog goes nuts.
And it's hysterical.
He runs over to the screen, growls at it, jumps up and stands along the TV stand and barks like crazy. And when the dogs go away, he races around the house looking for where the dogs went.
The other great thing now is that he's recognized sounds from ads featuring dogs. So even if he's not around and there's an ad with a dog on TV, he'll start growling and running in from out of the room.