Photographs don't have ethics, because they are pieces of paper with ink sprinkled on them.
People have ethics. If photographs are manipulated with the intent to deceive, then the photographer is unethical.
Paintings and other illustrations have nothing to do with it. When you have an art form that represents some idea of "objective reality," but that art form is necessarily produced over a more or less long span of time, then any intelligent person can deduce that what he is looking at is at best an approximation of that objective reality, because reality does not sit still to have its portrait painted.
Photographs, however, have since their inception been sold as the best representations of reality available to us. That's really the only reason anybody bothers to look at them. All the other sophomoric objections to that reality -- that is, that it's edited or cropped or whatever -- are again easily dealt with. We all *know* that a photograph doesn't represent a reality outside the photograph. So you have fifteen people in a street with protest signs, and you shoot a close-up that shows those fifteen people, then two things may happen: somebody may assume (incorrectly) that it's a small slice of life and that there are actually thousands of unseen people, or he could accept the reality of the photograph: that there were fifteen people in the street with signs. If someone makes the former assumption, that's his problem, because that's not what the photo shows. The photo isn't dissembling or lying, because it can't -- it's a piece of paper with ink sprinkled on it. The caption or accompanying headline might be, however, because it's a statement written by a person, and that person may have questionable ethics.
The ethical problem occurs when a photograph is substantively altered, but the person doing the manipulation attempts to retain its character as a photograph, and then either maintains that it is am image taken directly from a camera, or allows the viewer to believe that. (Belief is always the default, because the only reason people look at photographs is because of the long-standing implicit guarantee that this is a slice of reality. "This is something I haven't seen, and therefore I'm interested.") If a person substantively alters a photo and then claims or encourages a viewer to believe that it is a close representation of reality, then he's a fraud.
It's also necessary to note that there are all kinds of photographic representations of reality. In infra-red or other alternative light forms, or micro-photography, are objective, because what they present us is what the machine records; so is a long exposure. None of those forms attempt to deceive, they just are what they are.
The major problems with ethics comes in borderline cases. You have a blue sky but the news photographer deepens it to create a more dramatic image. Is that deceptive? Yes. You have a blue sky but the photographer deepens it because he's trying to make the scene as close to what he saw as he can. Is that deceptive? No. He's trying to get at the truth of the matter.
Unfortunately, in those borderline cases, you have to trust the photographer, and not all photographers are trustworthy. In fact, they may be pulled in two directions -- especially those photographers in competitive or free-lance positions who are working for news organizations. The two directions are: photographs that will satisfy the news desk's demand for drama ("If it bleeds, it leads") and the simultaneous demand that everything be "objectively true." The photographer's job may depend on *both* of these things at the same time, yet these things may be contradictory.
There's also an entirely different case, which doesn't really have much to do with photography. A photographer accepts a news position in which there are explicit rules governing the manipulation of photographs. Color must remain as recorded by the camera, the rules state. The photographer is free to change white balance before the shot, but is not allowed to adjust it in post-processing. The photographer then manipulates the color in post-processing to get closer to what he experienced. He is fired - not because the photo isn't more accurate, but because he violated the terms of his employment. Saying that the photo is "more accurate" is beside the point.
As far as 1a and 1b are concerned, I have no problem with either. But if 1b were represented by the photographer as "a shot I took last night," then he's an unethical fraud. If, at the bottom of the photo, there's a tagline that says, "Composite representation of the X lighthouse with the Milky Way overhead" then there's no problem...
In the case of "nature photography," the problem is as stated above: If you represent a photo is "as taken," and it isn't, then you're a fraud. The problem with way, way too many nature photographers is that they commit "minor frauds" (in their minds) to get sales. Is this photo as represented? "Yes, except that I took out Coke can and cloned in some grass where it used to be." Saying that is fine, but how many photographers would admit to it, if they thought a sale was on the line?