Photographs of Orbs: Are they proof or just dust?

SeattleGhost.com talks about ghost photography, specifically of orbs.

By some, orbs in photographs are thought to be spirits or ghosts caught on camera. Is this actual phenomena, or simply dust or particles captured on film? Dust can appear on cameras, the light from the flash is captured in the dust particle and it appears in the photograph as an orb. Dust, especially in an old building or abandoned location, is most likely to be present and can show up in photographs. For those who believe that orbs signify a paranormal occurrence the following is described; The orb has a nucleus and ridges, a glowing edge, and an almost solid quality about it. 

What is interesting for us, as ghost tour guides, is when multiple cameras get the same orbs in the same location. Also, there are places we have taken people to where photos taken on different days, in different weather, and day or night, show the exact same orb in the same location. (If you take a picture on the tour and want to send it to us, that would be fantastic: marketghosttour@gmail.com) That makes us really wonder about whether orbs are actual phenomena. 

Wikipedia offers an article about orbs. This is the quote about paranormal activity. "In addition to optical effects, orbs have also been considered in some circumstances to represent various kinds of paranormal phenomena such as light beings, aliens, extraterrestrial spacecraft, ghosts, or some type of elemental being. While there are scientific explanations for the appearance or orbs in some photographs, existing scientific theories fail to explain all such appearances. An example is the consistent appearance or orbs and other moving light phenomena in photographs at certain locations such as the ECETI ranch in southern Washington state near Mt. Adams. Orbs consistently appear in large quantities in photographs here regardless of the type of camera used, regardless of the time of day or weather conditions. The preponderance of orbs at such locations exceed current scientific explanations and remain unexplained phenomena."
I found a website that de-bunks orbs and I like the straight forward writing on it: www.prairieghosts.com
I also found a website that explains orbs as energy or spirit guides: www.paranormal.lovetoknow.com