I don't have any sources, But I've heard several claims that a photo can be edited in such a way that there is literally no trace it was digitally edited.

My question regards the usual digital photo, also I'm not asking about photoshop specifically but on any software tool.

[The motivation to my question is if this claim is correct then any digital image won't hold as evidence in court.]

From this motivation, one can draw in what sense "edit a photo" stands.

Is this claim correct correct? To what extent is this true?

[I will try to investigate where I've read this claim, but I'm not so sure I will find it]

EDIT: I see my question arises several ambiguities (which probably stems from my lack of understanding in this subject), I will address the subject of which editing I refer to.

In particular let me give some examples: planting people in photos, changing facial features of people, removing objects, modifying features of objects.

I know those examples are broad but I ask you to address those examples in the "intuitive" way, not in a general way.

I will edit this question to be more appealing, once I will see it addresses main concerns.

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    It's unclear what is meant by photo (a dslr photo? a scan? any digital image?), what is meant by "photoshop" (does this include custom tools?) and what is meant by edit (does changing a single pixel count as edit? a comment in the file?). Can you investigate this claim a little and provide a few examples, so we can address it properly? – Sklivvz Sep 17 '14 at 18:40
  • Any digital image could be modified without changing any of the metadata - the date taken, last modified date, etc. could all be the same even though the file has been altered. From there, it's just a matter of someone being able to modify an image well enough that you can't tell just by looking at it that there has been some modification. – Rob Watts Sep 17 '14 at 18:54
  • More than finding a precise source of the claim, what precise nature of editing to you have in mind? Suggestions for "concrete" examples of alteration that is relevant for many conspiracy theories discussed at this very site would be the removal or addition of image elements – Lagerbaer Sep 17 '14 at 19:30
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    Possible? It's certainly possible to generate the necessary stream of bits to produce a given file (image or otherwise) from nothing (and therefore possible to alter a given stream of bits to produce something different). Likely? That's something different entirely, for which I do not have an answer. – Brian S Sep 17 '14 at 19:39
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    I'll leave this just as a teaser, but removing objects from an image can be done using sophisticated algorithms: graphics.cs.cmu.edu/projects/scene-completion – Lagerbaer Sep 24 '14 at 16:49

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