First things first:
Or you should already take care of objects, unnecessary objects, main objects and other things, before taking photo, which will make photo better?
What is "better"? Is it a photo that you like more than others? A photo that I like more? A photo that we all like more? A photo that has fewer flaws? Flaws seen in which person's perspective?
Also, "better" has nothing to do with "more morally acceptable" - e.g. I would probably be a better human if someone put Einstein's brain in place of mine, yet this would not be very moral to me.
First, we would have to define what we consider as being 'moral' or 'immoral'. I guess this can be considered a broad definition that we could agree upon:
Those who use “morality” normatively hold that morality is (or would be) the code that meets the following condition: all rational persons, under certain specified conditions, would endorse it. [...] Definitions of morality in the normative sense—and, consequently, moral theories—differ in their accounts of rationality, and in their specifications of the conditions under which all rational persons would necessarily endorse the code of conduct that therefore would count as morality.
Definition of morality from the Stanford Encyclopedia of Philosophy
So in terms of photography...what is and what is not something that we all can agree upon? I guess most of us think that we should honor contracts - but are all contracts morally acceptable? The morality of an action has to be judged for every specific action.
The first thing that comes to my mind is the issue of composition - where is the difference between cropping the frame digitally vs. zooming in at the time of image capturing? Both have the same result. To add to xenoid's point: would it be less immoral just to push Mrs. Merkel out of the frame before taking the picture? How so?
But let us go through some cases in which I believe that editing is not immoral at all:
If in one of my model shots, you can accidentally see the underwear and/or some "naughty bits" and I only came to recognize that in post production - is it immoral to:
- break the contract with the model and publish the photos as-is?
- edit it slightly so that it is no issue?
- delete all the photos immediately and act as if they never existed?
There are of course more options and combinations of options to this, including "talking to the model about the issue" - I wanted to keep it short ;-)
A somewhat similar example be made with journalistic photos: Is it immoral to blur faces in shots of dissidents? Is it immoral to not blur them although it was an agreed upon term before taking the shots?
As you see, it is impossible to answer your question for each and every case, as every case needs its own evaluation of what would be morally right.
That does not mean that I think that the answers given here are bad in any way (some of them got +1s from me). I just want to say that defining what is and is not moral is incredibly difficult - and even more so with something as photo editing, which to my mind begins even before taking the actual shot.