Re: method to reveal photoshop manipulations


"sobriquet" <dohduhdah@xxxxxxxxx> wrote in message
news:1190755485.102473.27070@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On 25 sep, 22:59, Eric Miller <millereric_nosp...@xxxxxxxxxxxxx>
wrote:
The cyclist is part of both pictures, so it must be part of the
original.

Not true. Because the photos were taken from the same position, the
cyclist could have been added to either photo.

Logic dictates that if one of the two pictures is the original, and
the (same) cyclist is part of both images, it dictates that the
cyclist must have been part of the original image.

That is a truism and it is logical. If a=b and b=c then a=c. The problem
with stating that truism here is that it has nothing to do with the
conclusion that you intend it support. The question is not whether the
cyclist was part of both images; the question is which of the two images was
manipulated.

Only the elements
that change between the images as you alternate between the original
and the modified version are potentially not part of the original
image.


Ah, finally, the logical fallacy that is hanging you up here: begging the
question. This begs the question about what has changed between the images,
which is the ultimate question. I take your word that the changes are as you
describe, but logic does not dictate that result. The cyclist was in the
position portrayed in both your images at one time and an image was
recorded. That cyclist, in that position, could have been added to either
photo. That modification could have been done to make it appear that the
cyclist had not moved when, in fact, he had. In fact, you could have
modified the second image to keep the van and cyclist in the same position.
That fact partly addresses your question regarding the ability to
objectively determine if changes have been made. If a person could not
modify the exif data, but could modify the images, he could modify a
sequence of images taken minutes apart to appear as if nothing happened
when, in fact, a bank robbery (or any other event) took place.


The white bus has been edited out from one position and has been
edited in at an adjacent position.

Perhaps, but the "white bus" is from two separate images. This is
apparent by the fact that the occupants of the white bus are in
different positions in both images.

One of the white vans was part of the original picture and the other
has been copied and pasted from a nearly identical picture (where the
van and it's occupants were in a different position).
But as far as I can see there is no infallible argument that implies
which of the two vans has been edited out or was part of the original
picture.

Infallible arguments are few and far between, even when they support a
proposition that is later established as fact.

For instance, some people might falsely assume that since the
van is approaching the photographer, the picture of the van that is
nearest must be the one that has been edited in.


That would be a silly assumption. But many, if not most, assumptions are
silly.


The question is whether the white
bus was on the left or right of the cyclist in the original picture.

But that is a different question than the one that you originally posed and
resolves, as a given, that the cyclist has not been moved.

Eric Miller
www.dyesscreek.com



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