Since the introduction of digital photography, strange orbs of light, usually invisible to the human eye, have appeared on photographs.

Orbs photographs have been found on the older 35mm photography - but were not as prevalent.
I guarantee that if you check through your digital photograph collection, you will find one, somewhere.
Studies have revealed that orbs can be accurately reproduced by introducing fine dust particles into the air - so that's the answer then! - the digital camera flash magnifies and reflects the dust particle or water molecules in such a way that your photograph reveals an orb - but is that it? - Does that explain every unidentified image that our cameras pick up? - or is there still a phenomena that warrants further investigation?.
Having checked through my own photograph collection, I have enclosed a selection of orbs.

Orb 2 accurately mimics the type of orbs reproduced by dust particles.
Orbs 1 and 3 are more of a mystery!
I cannot support the popular claim that unusual orbs are manifestations of spirit - as there appears to be no evidence, other than personal interpretation and belief, to back up the theory.
Orbs have been photographed in reputedly haunted locations, but not exclusively. (In the case of the photographs submitted above, I have no reason to believe that my back garden is a haunted location).
The “paranormal” categorisation of orbs is interesting.
Paranormal studies are unfairly maligned and instantly dismissed by a large proportion of the population - probably due to an ever increasing unrealistic dramatisation of the subject on our TV screens, however, it has to be noted however, that despite all of mankind's huge technological advances and scientific understanding - there are still huge gaps in knowledge in every field of science. We are still a long, long way from truly understanding the world in which we live.
“Paranormal” anomalies highlight new arenas for potential investigation which could result in a greater scientific understanding of our world.
As the technology behind digital photography advances, we could be faced with an increasing number of unexplained lights and shapes in our family albums.
The digital camera gives us an insight into an increased electromagnetic spectrum which cannot be detected by the human eye.
We have viewed our world and based our scientific theories upon perceptions which are limited by human anatomy.
We only hear sound ,or see light emitted from a small proportion of a spectrum range which is potentially infinite.
Think of someone furiously blowing a dog whistle from a nearby concealed location - all that you perceive is your dog barking and jumping and going mad - for no apparent reason.
As our technological hardware and software advances, we get a glimpse into areas beyond the limits of our human anatomy - any unexpected results have got to be worthy of further investigation.
Orbs / light anomalies - don't dismiss them just yet!