I'll tell you what it could have been..
The girls in the first photo appear to be wearing heavy jackets & coats. So, I venture to say that the photos were taken in the late fall or winter. Your camera was cold and a misty condensation formed on the lens, or if a film camera on the film itself. Similar to when people that wear glasses come in from the cold outside. By the time you took the third picture the condensation evaporated.
If it was a digital, check your pictures after you take them. It would have been nice to have several pictures seconds apart to compare. If an anomaly is in one picture and not there seconds later you might have something.
Good ghost hunting!