Uncle Ghost Picture

"I am definitely not a believer in ghosts, but this picture taken by my sister, in my uncles home a few weeks after his death, really has me wondering. She outlined the mist form in the picture, and this form looks very much like my uncle. I was not there when the picture was taken so I don't know if anyone was smoking when it was taken. It does not look like smoke to me, but I'm not an expert. What do you think this is?"