Why would the lie? They seem so honest.
Dr. Novella was looking at a ghost photo and hit on some of the issues revolving claims.
First, yes people can and do lie. Not always, but it can happen. People sometimes like to be special, sometimes they want to show that their is magic and wonder in the world (regardless of the existence of plenty of wonder in our natural world), and so people just like to fuck with other people.
But there are other reasons (Arguably it is more common than the lie, but I have yet to see any numbers how it may break down.).
Sometimes people see something and just jump to and embrace a conclusion: ghost of a loved one, life among the stars showing itself to them, proof of a greater purpose to life and the universe. It could be true, but their perception bias leads them to see only one viable answer, the least likely one.
... The teenager, Kasey, says that she and the little girl, Penny, were the only ones home at the time. Perhaps, however, she was mistaken about this fact. Perhaps she simply did not notice the women who wandered into the room when she was focused on taking pictures of Penny.
There is such a thing as attentional blindness, which can be quite dramatic. Yes – people can simply not notice such things. I am sure you have seen pictures of people with items in the background appearing to come out of their heads. When looking at the picture it is obvious, but when the picture was taken the photographer was focused on the subject an not the entire frame of the picture.
There could also be something unusual going on – perhaps there was a picture of a person behind the girl, or it’s a reflection. Perhaps it is a purely photographic artifact.
What I always find interesting is when believers (just read the comments to this story) argue that an alternate explanation is unlikely, but then substitute the explanation that it is a ghost – as if that is not significantly more unlikely. See Occam’s Razor.