You stand looking out your window as the snow falls lightly. After a few minutes you start to leave when you notice the window has been fogged, slowly dissipating. You take a picture.
You reach out to touch your reflection in the mirror...nothing is there, only an image of you looking back. However, when you withdraw your hand, you notice fingerprints remain. You reach for your camera.
You come in out of the rain and walk to your bathroom to get a towel. You turn around and notice muddy footprints have followed you. You touch them and they're still wet. You look up at your wife. She's scared. Or angry. You're not sure which. You snap a photo.
What won't pass for the unexplained these days? The above scenarios all have easily recognizable natural explanations. But sometimes people can't find explanations so easily and they are quick to provide some alternate, supernatural reasons which, even in the absence of logic, lends some measure of certainty to their lives, even if that certainty revolves around a fantasy.
The Skeptic's Guide to the Universe has posted a recent video on ghost pictures...or more specifically, "unexplained" ghost streaks in photographs. Much like "orbs", these are nothing more than artifacts of photography but are perpetuated as unexplained mysteries by those who either do not understand how exposure works or are deliberately misleading the public.