Things I might need to reiterate

 I should probably reiterate that "demons" and "ghosts" are the same thing, and are human. They are the souls of the dead who serve Satan; and that's all the ones who are here, because they wouldn't be here if they didn't serve Satan, at least by default.

Satan is the god and creator of this world. We are all under Satan's jurisdiction, to a point, at least. The dead who chose Jesus go on to another place. The dead who are still here did not make that choice, and because of that, they are under Satan's authority, and serve Satan by default.

They're not all bad; but they're all subject to being influenced, or controlled even, by the others who are. Some who are here may have switched sides, in their hearts, at least, but they're still here for some reason, and therefore, they are still under Satan's jurisdiction.

They can appear however they want, when they choose to either transmit a mental image of themselves to someone, or appear in a photo. They often appear as inhuman creatures; as cartoonish imps, monsters, or animal-hybrids. It's even possible that some of them may have looked that way, but even if they did, they're humans, and most of them looked like anyone else you know. Most of the ones communicating with anyone (or haunting them) are fairly recently deceased; from the past few decades, or from the twentieth century, at least.

I often read posts in which people are asking, "Is it a demon, or a ghost?"
Just know that they're the same thing.
Sometimes people ask,
"Which demon looks like this?" and then describe what they saw.
Just know that absolutely any one of them could have looked like that. 

Also, ghosts/demons/earthbound spirits are not leftover energy, bad vibes, or unintelligent residual hauntings. There are some confused mediums out there preaching that wrong-thought gospel, so I'm trying to set the record straight.