I agree, although my dog's head is probably that big and he's a Rottweiler. When I first saw the teeth they looked like my dog's. I'll try and get a picture of him with his mouth open tonight.
Now that I look at the other pics you're probably right. I was judging by the size of the skull in relation to the ball cap. If that's not an optical illusion, that would be one huge head with the muscle tissue, skin and fur added. Even bigger than this one: (this is Max at around 1 year old looking my wife eye to eye. He's still just a skinny pup in this one.)
Here ya go guys. I looked at the different dog skulls mentioned and I think this is the match according to the eye sockets.
Might be a bigger dog like Great Dane or Irish Wolfhound which are the size of deer This is pictures of Irish Wolfhounds skulls http://frietsongalis.nl/wp-content/uploads/2009/06/GalisFig3.jpg
Well I reckon the consensus is that it's a dog. He was a long way from home. I'd hate to meet him in the dark (or light) woods, probably how he met his fate, happened upon a hunter.?.