How much digital manipulation can a photograph have?

[Written as comment on Hacker News in response to this article.]

I think it is slightly unfortunate that the topic of the photo triggering this debate is a controversial political topic with many contradictory truths, claims and counterclaims of distortion and deceit. In this case there seems to be legitimate journalistic photography of the event that should be the focus of any debate about the event itself.

The real issue with this photograph are whether the digital processing applied exceeded that which is appropriate for a photography competition. Specifically there seems to be a suggestion that it may be composite of different photos from the same event although that seemed far from proven to me.

What do people feel are acceptable digital edits to be applied?

1) Global filters/brightness/contrast/sharpening

2) Similar filters applied to local areas to to ensure all wanted areas are properly lit and visible

3) Actually touching up/smudging or otherwise directly manipulating particular pixels.

4) Actually combining different photos (e.g. you have ten photos but someone (different) has their eyes shut in each one so you grab one face and merge it back onto the correct body).

Personally I don't see a single clear line where you should stop so I think that it should probably be spelled out in the competition rules.