False positives are things that may have been considered paranormal but identified to be of a natural source.

Orbs are often considered to be paranormal however, the vast majority are natural in cause. Dust, pollen, lint ,moisture and reflections are the most common things to create "orbs"..

Streaks of light .This one was identified as a street lamp outside of the building. The slow shutter time of the camera and the slight movement of the photographer is the cause of this streak of "energy".

Mists

Breathing out when taking a photo in cold conditions is the cause of the above mists.

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This pic was taken by Tom Bunn at the Brigham City Train Depot.  This is his explaination...

Since the areas being photographed were darkened, the cameras were set for an exposure longer than "usual," about two (2) seconds.  Most exposures are quite instantaneous and able to freeze action, e.g., the exposures you would use in bright sunlight as very short (about 1/500 second).

 

An object moving across the camera's field of view in the dark would be imaged as a blur as it moves across the picture area as the exposure is being made.  This gives an impression of transparency, a ghostly veil, or long streaks of light.

In the case of Kelly's "ghost", she was close to and facing the camera as the exposure began, then she quickly moved away from the camera. 

This photo was submitted by Dylan. In the background behind the baby is what appears to be a man wearing glasses and a hat. The man turned out to be a plant in the background. This is a great example of paredolia.