Re: method to reveal photoshop manipulations

On 25 sep, 19:09, "Eric Miller" <millerericnos...@xxxxxxxxxxxxx>
wrote:
"sobriquet" <dohduh...@xxxxxxxxx> wrote in message

news:1190737274.789118.204840@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx







Suppose I have a picture and I modify the picture in photoshop to
remove an element in one part of the picture and add an element in
another part of the picture. Subsequently I save the original with the
same settings as the modified picture and I remove the meta-info
(exif, etc..) of both pictures with a utility (e.g. jhead).
Is there any method to more or less objectively determine which of
these two pictures is the original and which one has been manipulated?

Below I have two pictures for instance, one of which has been
manipulated. Can you guess/determine which one of them has been
modified?

http://www.ibbu.nl/~nsprakel/x.jpg
http://www.ibbu.nl/~nsprakel/y.jpg

My guess:

It appears that x.jpg has been modified by adding the cyclist and other
parts of the scenery from y.jpg. This modification makes it appear that the
cyclist has not changed position between the two images which were taken at
different times.

The cyclist is part of both pictures, so it must be part of the
original.
The white bus has been edited out from one position and has been
edited in at an adjacent position. The question is whether the white
bus was on the left or right of the cyclist in the original picture.
You can closely examine the difference between the original and the
manipulated image by opening them in photoshop (or gimp) in a single
document with each of the pictures on a separate layer and zoom to
100% or more visibility while turning the top layer off and on or
changing the blending mode.


Anyway, I think that in answer to your question, that the answer is probably
negative. I suspect that image manipulation is largely a subjective,
judgment call. But the cavernous abyss that is my lack of knowledge about
software and how changes to images may be analyzed by it should be taken
into consideration along with my opinion.

I do think that there is an objective means to determine that certain images
have not been manipulated, but that requires certain equipment manufactured
for forensic photography and doesn't really answer your question.

http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=389x1761730

(same as http://tinyurl.com/25tp6r )

But this method doesn't seem to work in this case. When I save the
manipulated image at a slightly lower jpg quality, subtract that from
the manipulated image, apply levels to make the differences between
the images visible, it doesn't reveal the parts of the image that have
been manipulated.
It probably only works if the images used to manipulate an image are
sufficiently different and not photo's that have been taken under
virtually identical circumstances.


Eric Millerwww.dyesscreek.com- Tekst uit oorspronkelijk bericht niet weergeven -

- Tekst uit oorspronkelijk bericht weergeven -


.

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