A recent article in the mainstream press mentioned mysterious orbs. The author offered an explanation, claiming that a single particle of dust on a camera lense will produce an orb. This claim is false. A particle of dust on a camera lens will absolutely not cause something looking like a mysterious orb to appear in a photo.
You can prove that by doing this experiment:
(1) point your camera at the ceiling, with the lens open;
(2) place a tiny particle like a bread crumb or a black pepper speck on your lens;
(3) take a photo;
(4) blow the particle off of your camera lens.
You will see that the photo absolutely does not show anything that looks like the mysterious orbs shown on this site.
A similar explanation is that mysterious orbs are dust particles floating in the air. This does not work for a variety of reasons, one of which is that the particles of dust in air are way too small to produce such an effect. You can read in detail about the exact math here. Outdoors an average-sized dust particle is only a hundred millionth ( 1/100,000,000) of the postage-stamp-sized area just in front of your camera lens. Indoors an average-sized dust particle is only a millionth ( 1/1,000,000) of the postage-stamp-sized area just in front of your camera lens. Such sizes are more than a thousand times too small to produce an orb that might take up more than 1/1000 of the area of a photo.