Well I have to say, I did Journalism at uni. And in PhotoJournalism we had this drummed into us.
BUT ... and a BIG but.
There is nothing illegal (as far as I can recall) about digitally changing a press photograph. It is more to do with a question of ethics. In particular, it is a breach of most Journalist Associations Codes of Conduct to do this.
The one that comes to mind is a photo of some bridge in Canada with an Olympic symbol that had been placed on it to celebrate Canada's bid.
As far as editorial stock goes, the site would say you are breaking their rules, and as such boot you from the site. However, I really do not think anyone could ever be sued for this.
To me that is the difference between a photographer and a photo-journalist. I do not know too many wedding photographers who do not airbrush the bride to make her look her best.
