This spring an alleged ghost photo made the social media rounds, with even USA Today taking a somewhat credulous view of the apparent apparition.

While most supposed ghost photos feature vague or distorted imagery, this one looks like a girl romping through the woods in upstate New York. The photo is clear and what’s unclear is why anyone was thinking it was a ghost.

There was some mention of a local legend about a girl having been killed by a train in the area, though no name was assigned, nor was there even confirmation such a tragedy had ever taken place there. The USA Today story also reports that a caller claimed the girl was his visiting granddaughter. This claim was anonymous so cannot be corroborated, but that still leaves us a long ways from any confirmation the youngster has risen from the netherworld. And why are ghosts are always said to be sticking around the farmhouse, asylum, or palace where they lived and died? They are seemingly freed from the laws of physics and could presumably travel the world for free, not even needing food money, yet they remain under self-imposed house arrest.

While this was a case of a clear image with a fuzzy claim attached it, many ghost pictures are the other way around: A fuzzy image accompanied by a strong declaration that it is someone who met an unfortunate fate in the area. Sometimes their names are offered, at other times it is just referred to as a nurse, soldier, maid, or other designator. In any case, the images are proffered as evidence we prance about in the afterlife, still fully clothed. These assertions are sometimes augmented with speculation that photography captures an intermediate dimension not visible to human eye. This claim remains void of any proof or an explanation of how this process would work, and is an instance of Tooth Fairy Science.

Whatever changes photography undergoes, ghostly images continue to be inferred. In the field’s earliest days, before film, photographers worked with glass plates which were cleaned after each photo and used again. If the cleaning wasn’t done thoroughly, faded remnants of the previous image might show up in subsequent photos. This would make for a freaky appearance to the uninitiated, which when it came to photography, described 99 percent of the country in the 1850s.

Also of consequence is that the advent of photography was simultaneous with the birth of spiritualism. Adherents of this faith felt the dead continued to exist as conscious spirits and could communicate with the living. To spiritualists, death was viewed as another realm of existence as opposed to being merely the permanent cessation of vital bodily functions. Interaction with these spirits was considered more likely thorough avenues like mediums and séances.

William Mumler fused photography and spiritualism, ironically mixing a scientific advancement and a religious regression. He created ghost photos and presented them to a gleefully gullible consumers eager to exhibit subjective validation and confirmation bias.

Alas, he was a 19^th Century Peter Popoff. Mulmer conspired with mediums, who would collect details about a dead person from relatives in exchange for half the profits Mulmer made from grieving family members. When he repeated these tales to the relatives, they were convinced he was in touch with the deceased’s spirit. Besides information about the dead person’s achievements and idiosyncrasies, mediums also provided Mumler with photos of the deceased. He then scoured his collection for someone whose appearance was similar and he dropped a faded image of that person into a second photo.   

His most famous client was Mary Todd Lincoln. I suspect finding images of this customer’s dearly departed would have been easier than in most of his cases. Mumler was eventually busted for his fraud, and while he was acquitted, he had been exposed and his career tanked. But the idea he promulgated lived on, and persons to this day continue to champion the idea that spirits are captured in pictures.

Many alleged ghost photos from the early 20th century resulted when someone inadvertently moved through a scene photographers were capturing with long exposure settings. This early photobombing created images similar to the multiple exposures on poorly-cleaned glass, but they also featured blurred motion or a repeated figure.

The double exposures continued with film-based cameras if the photographer forgot to advance the film. This was usually instantly recognizable as a mistake, but it infrequently would make it appear that a ghostly face or figure was looming.

These apparitions were consistent with an era of Dickens and Poe. Today, with the notions of auras, chakras, and an undefined New Age energy, orbs have replaced Victorian gentlemen and wailing damsels as the most popular poltergeists. An orb is usually explicable as being dust particles bathed in a camera’s flash, as opposed to it being Great Aunt Erma in aurora form.

Another frequent misinterpretation focuses on insects flying in front of or landing on security cameras. Probably the most-known instance of living six-legged creatures being mistaken for dead bipedal animals took place at an Ohio gas station in 2007. A blurry, mostly transparent image seemed to be hopping and darting around the cars and customers, and was the result of insects walking on the lens.

Even a camera strap partially obscuring the lens and being out of focus from the rest of the photo can appear ghostly, whatever that is. It’s hard to say precisely whether something is a ghost when we have never captured one, despite a decade of Ghost Hunters and hundreds of professionals engaged in precisely this pursuit. 

Such hunts are almost always done at night even though there’s no reason to suspect ghosts are nocturnal. It’s done for effect and to increase ratings. But if also done during cold nights, the visible breath can be combined with camera flash to create something spooky looking. This is where pareidolia comes into play, especially in photos that aren’t hoaxes. Hoaxes involve inserting an image of a real person into a second photograph. But with the orb, insect, camera strap, and cold-breath photos, the images are impossibly vague and in many cases it’s unclear what a viewer is supposed to be seeing until it’s pointed out. Even then, what is supposedly revealed is nothing more than half a face or part of an arm, and is often covered by smoke, mist, trees, or stairs. 

While a few ghost photos might be of a form resembling a human figure, the scarcity of these pictures works against the idea that spirits of the dead are being captured on film. If these really were ghosts, and photography captured an in-between land of the not-quite-living, not-quite-dead, one would expect to see ghosts every day on every hospital camera. This is not the case. Similarly, photos of battlefields and mass terror scenes are conspicuously apparition-free.  Photos taken at Waco, Oklahoma City, the World Trade Center, and Pearl Harbor should show a booming poltergeist population.

Instead, we have no ghosts from those locales, and the ones that supposedly show up in other places are the result of the effects of shadows, fog, exposure, sunlight coming through cracks in a forest, and similar factors.

For those who engage in deliberate deception, hoaxes are much easier to pull off with PhotoShop. At the same time, such advancements also make it tougher to fool multiple experts. Finally, if no answer can be found, that only means the photo is unexplained. It doesn’t mean that the default explanation is that it’s a ghost.