Snow (or rain) falling in front of the camera lens can reflect the camera's flash and appear as orbs - clearly not ghosts. These photos show how snowflakes lose their form when the flash hits them and as they strike a bright reflection of light.
We suggest that when trying to take paranormal photographs outdoors, it is best to do so when it is not raining or snowing. Also be aware of common causes of mists, such as snow melting in warmer temperatures (fog), waterfalls, fountains, creeks, etc., which can also produce false orb pictures.
Notice how the snow creates a lot of bright orbs as the camera's flash reflects off of them. Kathy Owen ran experiments for us, too (last 3 photos in the slideshow):
"The L.I.P.S. team (Lake Isabella Paranormal Society) headed out on a snowy night to take pictures of the snowflakes and to show us how snow can appear to look like orbs. Of course, snow can come in different shapes and sizes, but it can also give off the effects to appear just like orbs. My digital camera was set on auto mode with flash. These are some of the interesting photos we got that night."