So the secret of orbs is that they are all light reflected from an energy which the camera is unable to focus on. This is clearly seen in many unfocused sections in any photograph with background lights especially. This is called 'circles of confusion'.
As dust, moisture, pollen etc can show up on our images as orbs, the unfocused spirit energy also, I feel, is presenting as orbs in our images. This is 'confusing' and we need to keep an open mind as to what we are 'seeing'. I have explained other phenomenah and the energy that I have felt from orb images in my book Orb Insights and Inspirations - A Wonderland of Possibilities. A free preview is available from the tab on Fb page https://www.facebook.com/OrbInsightsandInspirations/
I will soon be posting more thoughts regarding the orbs, spirit or not.