Ghosts on cameras

Post summa summarum:
Is is not very probable that ghosts and other spiritualistic things do
not exist at all. Historically, statistically and, in the end logically,
a corn of truth exists.
Perhaps ghosts can be captured on camera. Perhaps not. Perhaps only
sometimes.
It cannot be proved either way, since the results of a shot cannot be
predicted and made to function under a simple set of laws. It sometimes
works, it sometimes doesn't.

Hence, the discussion is useless, since it can lead nowhere. People will
believe whatever they want to believe and for anyone holding the truth,
there is no reason to prove it.
People claim that you can catch ghosts or spiritual manifestations on a
camera. To determine whether this is rational, we need to know a lot
about how cameras work.
If you're interested, you can read the small fragments I had the
patience to collect.
If you're not interested, just grasp these two very basic things, which
is how much I understood of the whole thing.
In a traditional camera, the chemical substances on the film react to
the light it is exposed to when you click the button. This creates the
imprint - the picture.

A digital camera creates a pixel map based on the electric charge
generated when photons slam into a sensitive material. This becomes the
digital image on your memory card.
So, fundamentally, the physical light that exists in the world about us
is captured and stored - regardless of the technique.
The rational theory about energy and cameras.
Summary:
The human eye is not capable of registering the same width of the
light-spectrum as a camera, and can therefore not register the
appearance of ghosts; or,
The human brain does not pass on the information received through the
eyes to the consciousness.

A ghost is not captured on almost every picture taken because of three
possible reasons:
There are very few ghosts in the world; or,
All ghosts are at a few designated physical spots, where humans are
rare; or,
Cameras capture only ghosts which are dense, while the rest go
unnoticed.
The possibility of ghosts being able to control their density somewhat,
can open the possibility for them to "appear" in front of a camera - or
a person.
If ghosts are to be captured on camera, we must at the same time believe
that our physical eyes cannot convey to us what the camera can convey to
its film, or its "sensitive material".
This theory could imply that our eyes are not as good as cameras, and
that they aren't technically capable of registering the range of light a
camera can register.

It could also imply that information that our eyes perceive is not
passed on to our consciousness. It is generally known that our brain
registers millions of phenomena every second, from how your little toe
feels to the light of tennisball in the sun. In short, everything you
can direct your attention to, your "brain" registers. However, the brain
(or you?) selects a very, very small part of these things to pass on to
the consciousness - the thing reading these letters.
This implication is also adaptable to the fact that some people claim to
see ghosts, while others do not.

However, if information is lost in our brain and cameras succeed in
"seeing" ghosts because they do not, technically, have a brain... Then
any camera should be able to capture a picture of a ghost at any given
moment - given you actually find a ghost.
And the reason ghosts usually do not appear on photographs can then be
explained by the guess that there are in fact very, very, very few
ghosts around. Or that they hang out at specific places, where
consciousnesses in physical bodies rarely go (with cameras).
And, occasionally, when they feel like it, they take a stroll in a city
and pose next to some woman smiling in front of a camera.
It would also mean that all energy that is not manifested into physical
form doesn't exist except in very few places.

Since such a thing as a feeling can travel without any physical vessel
from one person to another, this theory does not hold.
It seems more probably that the energies in, let's say a city, is full
of turmoil, vortexes and all kinds of "spiritual" phenomena that camera
should be able to capture - if it can capture ghosts.
This however, could be explained by the thought that ghosts are more
dense than this general energy - and that a camera can capture this
denser form, but not the "less real" ones.
This also implies that different ghosts can be of different density, or
even that ghosts could control their density somewhat - making
themselves visible to a camera at will (i.e. posing).

The irrational theory of rejection.
Ghosts do not exist, and all pictures taken by cameras that show some
"super-natural" phenomenon are either a trick of the light ("orbs" (or
dust), "light-rays" (or camera straps) etc), an error in the camera or
in relation to the operation of the camera, or a conscious attempt by an
individual to trick his fellow men by forging his pictures after they
are taken.
The somewhat unlogical theory of lightning-ghost-posing.
Ghosts cannot be seen by cameras, unless they want to be seen. This
melds somewhat with the The rational theory about energy and cameras,
but it is not quite the same.
Here, we assume that the human perception and the camera perception are
the same.

Ways ghosts make their way into our cameras:
They "make themselves visible", or "densify" their presence the moment
the camera takes the shot. Not a moment before, not a moment after. This
produces the picture on the camera, but perhaps it is too fast for the
human eye to notice and remember. Ghosts could do the same in front of
humans, capturing their attention momentarily, imprinting a picture in
their minds - and sometimes they do.
Ghosts physically manipulates the camera. For example, in the case of
the traditional camera, ghosts change how the chemical substances on the
film reacts when it creates the film. Likewise, they could change how
the photons are "slamming into a photosensitive material." This doesn't
seem quite probable, since they would all have to be masters of physics
and math to do this at the speed required.

For the interested; some terminology:
Capacitor:
From Wisegeek.com,
A capacitor is a tool consisting of two conductive plates, each of which
hosts an opposite charge. These plates are separated by a dielectric or
other form of insulator, which helps them maintain an electric charge.
To understand the flow of voltage in a capacitor, it is helpful to look
at naturally occurring examples. Lightning, for example, is similar to a
capacitor. The cloud represents one of the plates and the ground
represents the other. The lightning is the charging factor moving
between the ground and the cloud.
Bayer mask:
From this site,

On a Bayer mask chip each pixel has one color filter, one next to the
other. The first row of pixels has green and red color filters (green,
red, green, red, green, red, green, etc. ), the next row has blue and
green filters (blue, green, blue, green, blue green, etc. ) and the next
one again green and red, and so on.
row 1: G R G R G R G R G R ...
row 2: B G B G B G B G B G ...
row 3: G R G R G R G R G R ...
row 4: B G B G B G B G B G ...
...
The raw "Bayer data" is essentially a monochrome image where each pixel
corresponds to only one specific color value. In order to get a color
image, the colors have to be "reconstructed" based on the Bayer data.
If you look at the pixels you will notice that each red pixel, for
instance, is surrounded by four green and four blue pixels. Also,
because there is an overlap in the color spectra of red, green and blue,
the available red value is at least in part the result of light in
another color. Based on the knowledge of what the colors and values of
those neighbor-pixels are, and based on the knowledge of the overlap in
the color spectra, it is now possible to work out (reconstruct) what the
green and blue values for that red pixel should be.

Please note that the actual color reconstruction is more complicated
than the method described here.

Traditional cameras:
A film is exposed to light.
The chemical substances on the film reacts.
This makes an imprint on the film - the picture.

Digital cameras:
A charge-coupled device, CCD (usually), is used.
It creates a pixel map based on the electric charge generated when
photons slam into a sensitive material.
From Wisegeek.com,

A charge-coupled device (CCD) is an integrated circuit, meaning it uses
multiple semiconductor elements on a unified platform to achieve its
goals.
The active components of the charge-coupled device in a digital camera
or other CCD-based cameras are the capacitors. These are linked in a
circuit, hence the term charge-coupled.
A capacitor is a basic electronics device that stores a potential
difference, or voltage, in the variance between two plates with equal
but opposite electrical charges.

A lens projects the image onto the CCDs. Each capacitor acquires a
charge proportional to the brightness of incoming light. CCDs are not
inherently color-sensitive, and to take color photos, a Bayer mask must
be employed to selectively filter light into designated pixels based on
color. Upon acquiring the charge, the capacitors begin passing their
charge to adjacent capacitors in a charge-coupled, daisy-chain fashion.
A register at the end of a capacitor array makes the appropriate
measurements, and a 2D pixel map is created.