Many times when an image has been posted, there are suggestions on removing parts of the image or adding features as toning or vignetting, in order to create a more balanced or more striking image. The digital technique has facilitated editing a lot, and it is easy to accept it as a norm, that the image is created in post production, just as we made our pictures in the darkroom, which has now been replaced by image processing software.
It is maybe a bit difficult for those that didn't use film and the darkroom as tools in image creation, to understand exactly where editing would not be considered manipulation, if we use a narrow definition of manipulation, and I tend to set the limit at where you alter image content. For example, in a picture of a dog, if you remove the leash with photo editing software, to show your subject without it. On the other hand, removing the leash before taking the picture would be another thing. In some genres of photography, also such altering of the subject might be objectionable, as for example tidying up a nature shot before taking it, removing straws, leaves, rubbish and such.
So for an image to be a "true" photographic image, in a documentary sense, no alterations can be done that change the content, although normal editing would include adjusting tonal curves, which is not manipulation in that narrow sense suggested in the previous paragraph. For some genres of nature photography, not even tidying up the scene is accepted, and captive animals or arranging dead animals is not accepted.
My own stance is that I won't ever present an image that is manipulated (narrow sense) without clearly stating what manipulation was done to it. It is a matter of honesty, and I cannot do those alterations that many people suggest to improve my pictures. I have a feeling that the image that's closer to the truth has a value in itself, even if it might in some way degrade the composition of the image. I'll show you an example here. The picture was taken outside our house in Santiago de Cuba, of our local butcher, a neighbour who makes a few extra bucks by slaughtering pigs in the street and selling the meat. The picture was taken with a p&s that has considerable shutter lag, and the man in the background, whose legs and carrying bag can be seen in the upper centre of the image was just entering the image on the screen from the left when I pressed the shutter, although lag made him appear rather much longer ahead when the actual photo was snapped. This image has had the tone curves altered in post production, which I don't consider manipulation, as it does not change the content of the image.
Now with digital technique, I can easily alter the image to something I envisioned when I saw him coming into the field of view. It is not only shutter lag that made him advance further than I saw it on the screen, it is also that the screen will not show anything until it has happened, until the person has advanced another step. So as the combination of view lag and shutter lag in a way ruined composition, it is rather easy to pull him back to where he was moments before in PP. So the second image is manipulated.
And this is some kind of standard I have set to myself regarding manipulation, that I won't change an image by removing or adding or moving elements in the image, even if it might enhance composition. Although the manipulated one is closer to what I saw when I pressed the release button, I prefer the shot that could be considered a missed one, if only because it is closer to the truth of when the shutter clicked.