There are many things that show up on camera that look like they are paranormal in origins but turn out to be natural phenomena.
This page will show you examples of such things
NB: when refering to entity we are using another word for ghost or spirit.
This picture was taken at night, the picture looks like it is full of orbs but this is just rain drops and moisture on the lens of the camera
This is a picture of snow taken at night yet again it looks like the picture is full of orbs but it is just snowflakes
This image is caused by motion blur, some people mistake this for a entitiy in front of the camera.
This is again an example of something being mistaken for orbs, this time it is dust
Smoke can often be mistaken for a entity manifesting on camera
This is a picture of the sun, this can sometimes be mistaken for an orb
This is a combination
of snow and cold breath, this looks likes orbs and a manifestation of an entitiy
This effect is caused by taking a photo through a window and getting a reflection
This is a shadow of a statue reflected on to a building at night, this could be mistaken for an entitiy
Finger over Lens
In the top left hand corner of the photo there is a finger over the lens, this could be mistaken for a entity
On this image there is a white streak going across the page this is actually a camera strap
There are many other natural explanations such as pollen, bugs and light streaks from over overexposure