This is an interesting article from Bryan Peterson on this issue. Thought I'd share
http://bryanfpeterson.blogspot.in/2010/06/every-photograph-is-lie-yet-within-that.html
He says: "Personally, I have NO problem with any image that has been dramatically altered, as long as it is 'believable' OR so obviously altered that it's not even a question e.g. fantasy, dream-like photographs. I don't mind the 'lie' that is created from a dramatically altered image, since I have felt for years that every photograph is a 'lie' anyway, but my problem with the dramatically altered 'lie' is that it can lead one to believe that a given landscape or cityscape really does "look like that" when, as it turns out, there is no such place on earth."
Thanks for the share! In my photo, such clouds do exist in that part of the world.