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Old 06-13-2008, 10:13 AM   #1
terrie
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Default Unique fingerprint?

There was an article in The Washington Post last week that stated "Every online picture has a unique numerical fingerprint..."

On first thought that made some sense because I figured it might be made of the DNS number plus perhaps some sort of numeric folder and file id but then I decided that this doesn't make any sense because if you move the image to a different website or changed the folder or the file name, the numerical id would change...

Sooo...does anyone know if the statement in the Post is true and if so, what is used to create the id?

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Old 06-13-2008, 10:39 AM   #2
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There was an article in The Washington Post last week that stated "Every online picture has a unique numerical fingerprint..."
I assume they're talking about the image itself. If two image files are really identical, they'll have the same hash checksum - for two images to have the same hash checksum by chance is a chance that's vanishingly small.

For instance, an MD5 checksum yields a 32-character string of hex characters: that will cover 16 to the power of 32 different possiblities with the algorithm ensuring that it's really, really rare for two objects to yield the same checksum result. And there are other checksum methods that give you even larger strings (like 128 or even 512 characters - do the sums ).

That's why such checksums are used to publish alongside downloadable software: download the file, calculate the checksum yourself, and if it's identical you can be sure the file hasn't been tampered with.

   
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Old 06-13-2008, 10:56 AM   #3
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marjolein: I assume they're talking about the image itself.
Yes...sorry I didn't make that clear...


>>If two image files are really identical, they'll have the same hash checksum - for two images to have the same hash checksum by chance is a chance that's vanishingly small.

What is used to create the hash checksum???

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Old 06-13-2008, 11:40 AM   #4
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What is used to create the hash checksum???
Something like this application.
There are quite a few to choose from, some are only good for individual files but others are capable of checking multiple files in one go.

   
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Old 06-13-2008, 12:18 PM   #5
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What is used to create the hash checksum???
I use HashTab which inserts itself in the Windows Properties dialog. It computes three different hashes, and when you plug any published checksum into the box it does an immediate comparison for you - very handy, and I always use that for downloaded software that has a checksum published.

HashTab is freeware by Cody Batt - to be found at http://beeblebrox.org/

   
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Old 06-13-2008, 04:06 PM   #6
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bo: There are quite a few to choose from, some are only good for individual files but others are capable of checking multiple files in one go.
Thanks for the link...

The article that I quoted from was about child pornography images and that investigators have created a database using the "fingerprint" of suspect images and it is being used as a filter to determine which providers are providing access to these images.

I'm not looking to use an app to check the checksum but am more interested in how the hash checksum is generated and is it really unique?

Thanks...

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Old 06-13-2008, 11:50 PM   #7
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I'm not looking to use an app to check the checksum but am more interested in how the hash checksum is generated and is it really unique?
Using software that implements the specific algorithm. If you change a single byte in the source file, you can be guaranteed that the resulting hash will be not the same. Just do the sums - how many different possiblities do you have in 16 to the power of 32? 16 to the power of 512? That's how unique you can get - not limitless, but very, very many different results.

   
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Old 06-14-2008, 01:33 PM   #8
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marjolein: Using software that implements the specific algorithm. If you change a single byte in the source file, you can be guaranteed that the resulting hash will be not the same.
That makes perfect sense to me but the question that I have is...

If you create an image using any of the imaging software available and save the image as let's say a jpg and upload it to some webpage, is there code built into all image processing programs that generates a hash checksum which one could check later using one of the programs you or Bo mentioned?

Or am I misunderstanding the process???

There is a part of me that is very uneasy about the idea that each of my images has some sort of unique fingerprint that could be used to track the image when I haven't deliberately used anything to generate that fingerprint--as in using the Digimarc system for example.

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Old 06-14-2008, 03:05 PM   #9
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Originally Posted by terrie View Post
If you create an image using any of the imaging software available and save the image as let's say a jpg and upload it to some webpage, is there code built into all image processing programs that generates a hash checksum which one could check later using one of the programs you or Bo mentioned?
No, the checksum is computed using an application. There are several different algorithms as well.
If you alter an image file even in a minute way the resulting checksum will be different compared to the original.
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Originally Posted by terrie View Post
There is a part of me that is very uneasy about the idea that each of my images has some sort of unique fingerprint that could be used to track the image when I haven't deliberately used anything to generate that fingerprint--as in using the Digimarc system for example.
It is only used to confirm that for instance a downloaded file is not corrupted or tampered with.

   
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Old 06-14-2008, 04:09 PM   #10
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bo: It is only used to confirm that for instance a downloaded file is not corrupted or tampered with.
Here in the States, the state of New York's Attorney General working with the National Center for Missing and Exploited Children has an agreement with Sprint, Verizon and Time Warner Cable that they will block access to newsgroups and websites that offer child pornography.

The National Center for Missing and Exploited Children has developed a list of child-porn sites and the NY state Attorney General's office "...also developed a system for identifying online content that contains child pornography. Every online picture has a unique numerical fingerprint that, once identified and collected, can be used to match the image anywhere else it is distributed. The database allowed investigators to filter through tens of thousands of online files at a time and determine which providers were giving access to child-pornography images." (source: The Washington Post)


So...that's what got me curious...

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