There are a wide variety of anomalies captured on camera that are believed to be representative of a ghost or spirit. The most significant of these findings are apparitions since they are the clearest pieces of evidence, and the most difficult to dispute. The descriptions below should help to get you familiar with some of the photographic anomalies you might experience while ghost hunting:
Apparitions - These are perhaps the most rare and solid pieces of evidence when it comes to ghost hunting. Apparitions are either whole or partial figures that take on the form of a human being, but are transparent in nature. Apparitions are like souls still attached to their physical experience, though they may also be aware that they have passed on. If they are aware of being dead, they may appear with a sign of whatever it was that killed them. For instance, if they were shot in the abdomen, they may appear with a wound on their stomach. Apparitions can sometimes be extremely vivid and rich in detail. Sometimes specific facial features even appear, and they may appear wearing the clothing that they knew in the time in which they had lived. Apparitions are an extremely rare find but are one of the most solid pieces of evidence a ghost hunter can capture. If historical photographs of people who once lived in a now haunted house are available, then the apparition can be compared with those real photos in an attempt to identify who it is that might be haunting the location. Alternatively, apparition photos can be extremely useful in coo-berating witness testimony. For example, if witnesses claim to see the image of these ghosts from time to time, it might help to take the photographed apparition and place it in a line up with a series of other apparitions and see if they can point out which apparition looks like the one they've been seeing. If they can clearly identify the photograph of the apparition as being the one they see on a regular basis, then you have a very hard piece of evidence to back up the claims of a haunting.
Ectoplasm Mists - Ectoplasm is a cloud that appears like an electric vapor. It is often white, gray, or transparent in color and appears in photographs that are believed to be by ghost hunters, spiritual energy. Ectoplasm may look like a web of electricity and can have some natural explanations as well as paranormal. For instance, if the photograph is taken outdoors during cold weather vapor from the photographers breath as well as fog, smoke, or any other naturally occurring vapor can all be misinterpreted as ectoplasm. Thought not as clear of a piece of evidence as a photographed apparition, these still hold a lot of significance when all explainable causes have been removed from the equation.
Orbs and Lights - Orbs are circular, semi-transparent discs that appear in photographs from time to time and are believed by some ghost hunters to be indicative of a ghost's spirit or energy. From personal experience, I have found orbs appearing in my own digital photos as a result of dust, pollen, or other debris in the air. Orbs are much more common in digital cameras today and can easily result when tiny particles in front of the lens reflect the light of the camera's flash. Although there may be paranormal significance to many orbs, and many ghost hunters believe them to be noteworthy, I have come to find that they usually have an explainable cause that is usually physical.
Shadows and More - Other photographs of ghost can include a whole plethora of other anomalies from shadows to lights to funnels and rods. All of these anomalies could have natural explanations as well as paranormal, so it helps to do you research and apply critical thinking before making a claim that the photograph might contain evidence of an actual ghost.