Mists

Ectoplasm has been studied for years, starting with mediums who would spew it out of their mouths at seances. There have been many misty photos taken that are assumed to be evidence of supposed ectoplasm or the material of ghostly phenomena. It has also been recreated by simply exhaling in the cold while taking a photo, or by smoking while doing photography.

Tunnel Mist:

There are a few reasons I believe there to be something authentic in these photos. For one they are taken underground in tunnels whose temperatures do not vary very much and stay around 50 - 60 degrees. Also all the other pics taken in the same area on the same day are completely clear of mists. If this were due to breathing, there would be some evidence in other shots.
All I did to the images on the right is to lighten them up and bring out the detail using levels in Adobe Photoshop. This does not change the content, merely how the colors and data already in the picture are displayed. Some say you can see the arm and shoulder of a woman in the lower left and a black hand in the lower center.
The photo on the right is one of many taken the same day. There is no mist at all as far as we can tell.
If you look at the pic above it actually looks like it might be dirt on the camera, I can not be sure. Notice the granular aspect almost as if there are a billion orbs jumbled together. I am rather skeptical about this one.
This one above was also taken in the tunnel systems. Note that the mist ends sharply on the left side, it has definite boundaries. According to some sources on ghost hunting this is one possible indication that this may be more than breath and no one was smoking.
The picture to the right was also taken in the same tunnel. Note that there seems to be a bright center to it.