Many of us have seen photographs with mysterious "orbs" of light floating about in them, or what appears to be a light zig-zagging across the photo. Most people gasp and declare they have photographed a genuine spirit in their livingroom, then show it to all of their friends and family.
Sorry, folks. Very very few spirit photos are "authentic."
ORBS:
While it can be disappointing that an orb is not really our great aunt Matilda back from the dead, the actual conditions required to produce an orb are really quite interesting.
Orbs of light in photographs are caused by light from the camera's flash reflecting off dust particles and/or moisture in the air. Interestingly, the particles must be within 1-4 inches of the camera lens to register and are too small to be picked up by the auto-focus; this produces a small flash of light back at the lens that is out of focus and appears large in relation to the rest of the photograph. If there are a lot of people moving around, there can be anywhere from a few to a hundred orbs in a single room are particles are stirred up. We can only see these particles when light reflects off them, as "dust motes" swirling in a beam of slanting light, or the flash of a camera.
Some people believe they can see faces in the orbs. One of the quirks of the human mind is that we a genetically wired for facial recognition; it is a survival instinct that goes back for millions of years. They are also designed to try and find order in chaos. In other words, our brains are programmed to that an a random shape and see it as something we recognize. Have you ever looked up at the clouds and said "Look, it's a bunny!" Rorschach (ink blot) tests are a perfect example of this phenomenon.
An orb can seem to appear in several different photographs as it is swept along in the tiny air currents created when we move and attracted to the static electricity of the camera. It's not following the person in the picture, it's following you!
If you see hundreds of orbs in a photograph, you might have step up your cleaning. If there are only a few, don't worry; there are billions of particles in the air all the time, especially during pollen seasons, perhaps more if you live near a busy street or open filed.
MOVING LIGHTS
Similar to orbs are the little wavy lights that sometimes show up in a photograph. These are cause by tiny hairs or fibers in that same 1-4 inches away from the lens. The flash reflects off the fiber and produces what looks like a spirit zipping through a room. Because of the closeness of the fiber, it is out of focus and blurry, and our minds associate blurriness in and otherwise crisp image as movement. Fibers are usually not straight, being either wavy, curled, or sometimes bent at sharp angles. And because it would probably not be exactly parallel to the lens, the light reflects more brightly off the closer end of the fiber. The resulting effect is a slightly blurry light with a streaming tail.
So, sorry, folks! Unless your picture was taken without the use of a flash or light coming from behind the camera, what you have is a very interesting photograph of a dust partlicle or wayward fiber.