Okay, I'm going to go out on a limb here and put my amateur opinion in on the part about 'not seeing them on the first viewing'

I think you may have a valid point about getting acquainted with the photo first, because mentally you need to recognize and remember the contents of where and what is in the photo, so you're able to discern what normally shouldn't be in the photo.
Right?

Here's my amateur opinion...
Maybe it takes a bit of time for some of the mystical beings to develop on a picture? Like a slow imprinting of sorts...
I know, it's far fetched... but, it could be...

About the beings in your images... maybe it's everything you mentioned. Maybe all or some or one of the beings are there.
It's kind of like taking a picture of a park filled with peoples and puppy dogs, squirrels and kids, rabbits and ants and birds and well, you're bound to catch one or more of them in a shot or two.

I cannot define the anomalies that I see in any pictures as spirit or flesh or etheric(?) and that is why I use common references... but it doesn't mean that they are not there. I hope you and Chriss are not offended when I use basic reference to the images and anomalies, I mean no dis-respect to you.

Your Gnome's a fun looking little fellow and I'm glad he stopped and posed for you to take his picture. The two or more wee ones off to the side are interesting, you can just almost make them out. Goodness, they do have great camouflage.