
Forensic analysis of recent Victoria's Secret photo - aditya
http://www.hackerfactor.com/blog/index.php?/archives/322-Body-By-Victoria.html
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davi
I didn't know what "Error Level Analysis" was. So:

'Error level analysis (ELA) works by intentionally resaving the image at a
known error rate, such as 95%, and then computing the difference between the
images. If there is virtually no change, then the cell has reached its local
minima for error at that quality level. However, if there is a large amount of
change, then the pixels are not at their local minima and are effectively
“original”.'

From <http://www.hackerfactor.com/papers/bh-usa-07-krawetz-wp.pdf>, a lot of
interesting stuff in there.

~~~
NathanKP
That reminds me of this interesting video which shows digital decay and JPEG
data loss in action:

<http://vimeo.com/400918>

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adriand
I would love to see an analysis like that of this photo I first posted to my
blog ([http://socialtech.ca/ade/index.php/2008/03/beware-the-big-
ba...](http://socialtech.ca/ade/index.php/2008/03/beware-the-big-bad-black-
wolf/)) which generated the usual claims of "Photoshop" on Reddit, until I
posted the original version, which kicked off many more claims that it was
'shopped
([http://www.reddit.com/r/reddit.com/comments/6byul/to_all_the...](http://www.reddit.com/r/reddit.com/comments/6byul/to_all_the_photo_experts_on_reddit_who_claimed/))

Even though, to the best of my knowledge, the photo is 100% real.

~~~
ErrantX
Im willing to bet there is some tampering going on. The body looks nothing
much like a wolf - more like a large dog.

If you fiddle with the levels in Photoshop that section does look really
suspicious (though Im no expert).

~~~
heyitsnick
I'm a gambling man (as my profession). I will offer you (3:2) - my $3 to your
$2 says this photo is real. Let me know how much you want to bet, I'd accept
someone reputable on HN will escrow. Would you trust the author of this
article as the arbiter of the wager, using similar techniques as the
Victoria's secret photo?

[I have no expert knowledge on photos, wolves, or the photographer in
question. But I like a good bet, especially in the pursuit of science!)

~~~
logicalmind
How will you define "real"? Clearly the representative set of bits that make
up the image are not "real". If you're attempting to determine whether the
underlying scene was real then this photo alone may not be the best evidence.
If you're trying to determine whether the image is original and unmodified,
then you have already lost. The image is modified when the picture is saved on
the camera itself and then any time the image is saved in any other program.

If you clarify your definition of "real" then your bet may become more
enticing.

~~~
heyitsnick
ErrantX said "I bet there's been some tampering going on". That's what I was
referring too. As is the theme of this thread. I'm not getting in to the nitty
definitions of the what "real" or "tampered" means because I think we all know
what is being discussed here.

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johnnybgoode
The two pictures the author showed after saying, "Here are two photos of the
same model" are of two different women. I'm pretty sure about this, because I
know who the first woman is. So it appears he did catch them on some things,
but he's made at least one mistake himself. Maybe someone else will know if
this led to any other mistakes on his part?

~~~
BRadmin
He changed the example pic, adding:

"[Update 2009-12-27: There was some debate whether the second picture was the
same model. I have changed the second example.]"

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baguasquirrel
<http://en.wikipedia.org/wiki/Principal_component_analysis>

When I read that he used PCA to detect that they modified her bust, I really
couldn't believe it. That is really impressive.

edit: I guess I should add a little background. PCA was used a good bit in
computer vision (and data mining in general) when I was in school. You
typically don't see it mentioned outside of those contexts.

~~~
nostrademons
PCA is used a lot in the financial industry. You can guess how it might be
useful there...

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jgrahamc
See also [http://www.jgc.org/blog/2008/07/photoshopped-iranian-
missile...](http://www.jgc.org/blog/2008/07/photoshopped-iranian-missile-
launch.html)

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barmstrong
I don't understand the criticism really. I would expect Victoria's Secret to
photoshop pictures.

~~~
NathanKP
It isn't about criticism, it is about forensics, using reasoning and computer
algorithms to figure out what people did. It is an intellectual challenge, not
a criticism.

~~~
ghshephard
Small Nit - but the use of "Criticism" does not always mean the pejorative:

From: <http://en.wikipedia.org/wiki/Criticism>

"The word critic comes from the Greek κριτικός (kritikós), "able to discern" ,
which in turn derives from the word κριτής (krités), meaning a person who
offers reasoned judgment or analysis, value judgment, interpretation, or
observation . ...

~~~
d_c
Indeed!

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tetha
Besides the very interesting analysis, is anyone besides me disturbed by her
face in the various analysis images? It looks really, really disturbing in
some pictures.

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grinich
This was used as an example in a short lecture about JPEG compression in one
of my classes this term. Here are the slides if you're interested. They give a
basic overview of perceptual coding and the 2D Discrete Cosine Transform.

[http://web.mit.edu/6.02/www/currentsemester/handouts/lecture...](http://web.mit.edu/6.02/www/currentsemester/handouts/lectures/L24.pdf)

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tvon
If the "ELA" indicates edited regions, why is the region where the most
obvious change happened (the bag) one of the darkest?

I'm also not convinced on the lightening of the skin tone. The lighting is
entirely different in both pictures, and I have friends who have shifted tone
more than that after a summer of tanning. (edit: her hair is much darker as
well)

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arithmetic
This is enlightening! I'm an amateur photographer who likes to post-process
some images (mostly tweaking contrast, brightness and the hues). This post
taught me quite a bit on photography forensics.

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NathanKP
Very brilliant, including the followup. This is forensics at its best.

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nshah
Hm... If only people could see the pre-process images...

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alexkay
Follow-up:
[http://www.hackerfactor.com/blog/index.php?/archives/329-The...](http://www.hackerfactor.com/blog/index.php?/archives/329-The-
Secret-is-Out.html)

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xcombinator
I love the article, and the Sherlock Holmes analysis too:

-Ohh, let me see... a professional photo could be manipulated by Photoshop or Gimp...

-mmmmm. It's photoshop what had been used.

He is truly a genius!!

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dmarshall
Is it just me, or does anyone else feel like it would have been much more
worthwhile to use an example that actually might have been 'tampered' with,
and not edited in post-production? Geeks and their VS--wonder what he did with
the lingerie catalog...

