The green colour of these flare orbs, somewhat ironically, comes from the microscopically-thin anti-flare coating on the camera lens. (But if this coating were absent, flare would wash out almost the entire image.) Also, the light source doesn't have to be visible in the photo to cause flare, but the flare tends to be more dramatic when it is.
If you don't want lens flare in your photos, try shielding the camera lens from the sun or other bright light with your hand, casting a shadow over the front of the camera. If the sun is visible right in your shot, like in these examples, you won't be able to cut out the flare. If you're shooting with a DSLR camera and you have a lens hood (lens shade) then use it! But do not look at the sun through the optical viewfinder as it may permanently damage your eyesight.
Another distinguishing feature of flare orbs is that you can draw a line through the centre of the photo (if it is not cropped in) that connects the flare to the light source. This is not always exact but is still a good indicator that you're looking at lens flare rather than something paranormal in origin.
Besides lens flare, the main cause of orbs in photos is backscatter, sometimes called near-camera reflection. This is when a flash or LED light positioned close to the lens strikes dust, raindrops or other small particles floating close to the lens, causing bright highlights that reflect back into the lens are are captured out-of-focus (because they're so close-up to the lens). These show as translucent globe-shapes that some still believe are early-stage spiritual manifestations.
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