Um...I don't wanna freak you out!
but, I remember seeing this picture on the net (from one of those ghost sites that have candid paranormal pics on them) when this guy was smoking a cig...And a face came up in the smoke (looked like a demon! Clear as day!). My guess was that whatever that enitity was, it was standing right there and maybe the smoke got in its face and formed it in the smoke?
Kinda creepy if that is what happened in your picture...
Hate to sound like a dork or something lol, but do you have any hauntings at your place that you know of? Sorry I'm a huge ghost believer...i've had many experiences before and a few were awfully scary.