Orbs
The Skeptics View
Skeptics of orbs claim that they can be a number of different things, some of which are dust particles in the air reflecting the light from the camera flash, moisture or water droplets, a dirty lens, or a fault in digital cameras.
The Believers View
Believers are of the opinion that orbs are some type of energy, be it spirits a dead folks, angels, fairies, or even energy produced by living people.
Our Findings
Although we cannot tell you with certainty what an orb is, I suspect that they are all of the above from both believers and skeptics depending on the circumstances.
At times you may capture dust particles, pollen, etc. These orbs will look kind of dead and have concentric rings in them. What I call spirit orbs glow brighter, and may have a busy pattern in them, or even faces. Pollen orbs tend to show up as small green orbs.
When people run energy such as Tai Chi, or other energy work, orbs tend to show up for a short while. Rather than that being caused by the living person's energy, I think the orbs are drawn to it. When you take several shots in a row of someone doing energy work the orbs seem to be approaching the person as if to see what they're doing. Once their curiosity is sated, they go away again.
Another thing interesting about orbs is that they will usually appear for a pic if you simply ask them to. I usually address them as Orb People, and at least one will usually show up in the photo shot at that time.
So to prove this to yourself, take a picture, then without moving, simply ask the orb people to show up so that you can take a pic of them. Sometimes you have to lighten the picture in an art program like Photoshop to get to see them if they're faint.
I have also photographed several haunted objects and asked for the spirit residing in that object to show itself for a picture. I have gotten orbs for the most part, but in one shot of a haunted doll, there is a full body apparition with the orb. See pic.
There are different types of orbs, some which are very bright and show faces in them. What makes it more perplexing is that some orbs have multiple faces in them, including those that look like animals or other non-human species.
Some people can see orbs with their naked eyes, and tell you exactly where to point the camera and get a good orb shot. If they were all dust, moisture or faulty cameras, this would not be possible. We are fortunate enough to have a member on our team capable of seeing orbs.
Cameras Matter
The resolution of your camera seems to determine what type of orbs you will get. A lower resolution camera seems to get more orb shots than a high resolution camera. Some cameras will periodically record orbs as diamonds or shields, too. See pic.
A high resolution camera may not pick up as many orbs, but seems to pick up details that the lower resolution cameras miss, such as faces. See pic and here for comparison.
Orbs have been photographed with film cameras, but it is a rare occurance. I think that digital cameras may be capable of "seeing" things that film cameras and most people don't see. Some modern camera's have been "fixed" to where they will not pic up orbs, since some photographers have found orbs in their shots to be a nuisance.
I use a high resolution camera, and seem to have the best luck getting orb shots in the dark and outdoors. When I take indoor shots, the flash is so bright, that it makes it hard to see an orb if one were to try to pose for the camera.