Orb

FACTUAL ANALYSIS: While it's impossible to entirely rule out the possibility that some photographs of orbs are paranormal in nature, it's a phenomenon that is so common and so easy to reproduce that photographic orbs are generally considered inadmissible as evidence of paranormal activity.

'Orb' is the name typically given to a specific type of photographic anomaly that manifests as a white circular feature, often appearing in images taken during paranormal investigations but sometimes also in photographs captured under other circumstances as well.

Orbs can show up pretty much anywhere, especially in people's houses or in old buildings which adds to their reputation as evidence of a paranormal presence.

The term 'orb' can also refer to glowing (or moving) spheres of light either directly witnessed or captured on video footage, usually during paranormal investigations.
Backscatter

The vast majority of orb photographs can be explained by way of one word - dust.

There are almost always particles of dust floating in the air, especially indoors. When a photograph is taken using the flash, the light will often reflect off these dust particles before being picked up by the camera, producing anomalies in the resulting photograph. Because these dust particles can also be close to the camera, it is not uncommon for them to appear blurry and out of focus.

If a photograph is taken in a room with a very large amount of dust in the air, there can sometimes be a veritable snowstorm of orbs in the image. It is possible to reproduce this effect by taking a handful of dust and throwing it in the air just prior to taking the photograph. In dusty old buildings, even the act of walking around can kick up enough dust to make this happen.

Orbs are particularly common in photographs taken during paranormal investigations because the locations being visited will often be old and dusty and the investigation will often be taking place in dark or dimly lit rooms, requiring the use of a flash to capture images.

Other things can produce orbs in photographs too. If you are outside, water droplets in the air can create the same effect, as can insects, particles of pollen or plant matter, sand and much more.

Note that this explanation also applies to night-vision images, the only difference being that the light being reflected off the dust particles is in the infra-red rather than visible part of the spectrum.

Some have argued that if you zoom into the center of an orb, you can see a face, however this falls firmly under the category of pareidolia, even more so when you consider that zooming in creates digital artifacts that can be particularly visible in the orbs themselves.

Due to how easy they are to reproduce, orb photographs are generally inadmissible as evidence of the paranormal.