We can measure the angle between any two lines of sight. This is often called the "visual angle", or the "angle subtended at the eye", or the "angular size" (when the two points are the extents of the object).
Importantly: this is entirely independent of the Field of View of the camera, or the eye.
A photo is flat. How we go from the real world to a flat surface is "projection" - which is literally like what it sounds like, projecting light onto a flat surface, like a movie projector projects an image onto a screen.
I'm beginning to realize some of the challenges in image interpretation. Your example was a great help. Here I kind of turned it around.
Suppose I'm watching a landscape where I see five tall buildings in my 60° horizontal FOV. They are in different distances but the angular spacing is the same 15°. I take a photo of the five buildings with some scenery on both sides. The focus is at the middle building.
In the nature I saw the buildings at the same angular distance 15°. So I might expect that they are equally spaced in the photo too. But they are not. If the distance of the outermost buildings 1 and 5 in the photo is 10 cm, the distance between the buildings 3 and 4 is 2.32 cm and between 4 and 5 it is 2.68 cm.
So just looking at the photo is hard to reason what the eye in reality saw. But can even the eye see "the reality"? In this respect, yes, because the human retina is not a flat disk.
In my previous post was an example "Tracy in ISS looking at the horizon". There I asked if the curve picture in Walter's calculator corresponds to what Tracy sees through the window. Now I think this was a little silly question, because a flat picture can never fully correspond what human eye sees.
The proper question could be: Are the options in calculator now correct, so that the curve picture corresponds Tracy's view the best possible way. There were other questions too. I would be thankful if you could comment them briefly. I guess it might help other uncertain readers too.