I've already found a site that covers non-UK phenomena. It was (ahem) in the sidebar here, the Paranormal Review, which covers a lot of US-based reports. I really should check my own links more often.
Back to pareidolia. Here's a photo from the Paranormal Review. Can you dismiss this as pixellation? As an interplay of light and shadow? If so, why? (The Hampton Court ghost below it has been shown to be a hoax since that was published. This one has not been.)
Note that the image of the ghost is incomplete, and that it shows almost as a phosphorescent outline, as if it's made of glass and lit by a light source we can't see. Entire apparitions, in full colour, are extremely rare as far as I know, although such apparitions would pass for real people unless you tried to touch them so it's impossible to be certain. This incomplete, almost two-dimensional image is typical of most photos and allows them to be easily dismissed as faked, Photoshopped (you could do far better than that with Photoshop, really) or just good old pareidolia. Once you have a scientific sounding Latin name for something, one that sounds like a medical condition, it's a weapon too irresistible to use. It's appearing in debunking reports everywhere.
It is rarely correctly applied, however. 'Faces' in treetrunks or rocks are more correctly termed simulacra, and Fortean Times has a collection of these. Some can be amusing, some can be revolting. If I had drunk most of a bottle of fruit punch and then found this, I would not be considering whether it might be a mould. I'd be too busy being violently sick. Then I'd take it to someone to get it checked. It was a mould, but how many could tell that at first glance? It's not pareidolia. This is not an imaginary image superimposed on a noisy background, it is a three-dimensional object that looks like something else. It's a simulacrum.
As is the rock that looks like a bigfoot on Mars. A British astronomy magazine published the entire Mars Rover image, in which it is clear that the 'bigfoot' is about an inch or two tall, is three feet from the Rover, and is a rock. Here, a sceptic uses the term 'pareidoliacs' to refer to this simple act of the mind as if it were a disorder. It is not. Everyone's brain does this. He also uses the sceptic's tactic of equating a pareidolic image with delusion, as if he cannot see it himself. He can. I know it's a rock, he knows it's a rock, but anyone who has seen only the severely clipped version of that image does not know for sure it's a rock. They are fooled by perspective, not delusional. They are not 'pareidoliacs' and neither are those who deliberately clipped this image to produce the hoax because no such condition exists.
Here again, pareidolia is elevated to the status of a neurological/psychological phenomenon, when it is simply normal brain function.
You aren't sick if you see Elvis in a piece of toast. You aren't deluded unless nobody else can see it. That does not mean Elvis goes around haunting toasters. It means that the specific pattern of hot and cold areas in the toaster along with the specific distribution of moisture and protein in that slice of bread combined to produce an image that looks a bit like Elvis. Everyone can see that image. It's a simulacrum.
When you stare at an untuned TV and you think you make out a face in the fuzz, that's pareidolia. Nobody else can see the image you see, it's just your brain trying to make sense of static. Others might see faces but they won't see the same thing as you. You can't photograph it because it's not there. It's in your mind. It's pareidolia. We all do it, it's natural.
Water seeping through concrete and then running down will often fan out. The dirt and minerals it carries can form a simulacrum of a cowled monk, or the Virgin Mary, or perhaps the Grim Reaper. Rocks and trees often form shapes that can look like faces to the mind that's looking for faces - and that's everyone's, believe it or not. They are not supernatural. They are simulacra.
The thing is, 'simulacra' doesn't sound as scientifically official as 'pareidolia'. The former describes a shape while the latter sounds like there's something wrong with the person who sees it. That's quite a powerful put-down, it's easy to equate wrongly with 'delusional' and it's one step from calling the claimant insane.
Simulacra are entertainment. Pareidolia is a natural function of the human brain. They are different things and neither is supernatural. Using pareidolia as if it refers to a form of insanity is resorting to dirty tricks, and if sceptics are so certain of their position they should not need to do that.
Pareidolia and pixellation are the two main tools of the 'debunker' who feels no need to explain their position further. Yes, many - I'd go so far as to say most - images are not what they seem, but if they've been filmed or photographed they are not cases of pareidolia unless only one or two people see them. They might be simulacra.
There is, of course, the one possibility that these sceptics dismiss from the outset. Before they've seen the image. Before they know it exists. Even before the photograph is taken.
The possibility that it might be real.