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Thread: NYT Article

  1. #1
    Senior Member dbutler's Avatar
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    NYT Article

    Nicholas Wade has an article in the Times about faking photography. I thought this was interesting:

    "He and Dr. Rossner plan to add software tests being developed by Hani Farid, an applied mathematician at Dartmouth. With a grant from the Federal Bureau of Investigation, which is interested in ways of authenticating digital images presented in court, Dr. Farid is devising algorithms to detect alterations.

    His work has attracted interest from many people, he said, including eBay customers concerned about the authenticity of images, people answering personal ads, paranormal researchers studying ghostly emanations and science editors.

    For the latter, Dr. Farid is developing a package of algorithms designed to spot specific types of image manipulation. When researchers seek to remove an object from an image, such as a band from a gel, they often hide it with a patch of nearby background. This involves a duplication of material, which may be invisible to the naked eye but can be detected by mathematical analysis.

    If an object is enlarged beyond the proper resolution, Photoshop may generate extra pixels. If the object is rotated, another set of pixels is generated in a characteristic pattern. "
    Dee
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  2. #2
    drg
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    la recherche de trolls drg's Avatar
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    Re: NYT Article

    The current consensus on this falls somewhere between detecting alteration and knowing via algorithms including but not limited to simple checksums and CRC to far more complex public key signatures what was there in the first place. The idea being that if your camera generates a unique number and modifies some portion of the data in a 'special way', encryption in other words, that if the image is modified it will be instantly detectable (O.K. a few millions cpu cycles perhaps).

    This assumes that the photographer keeps the original to backup any evidence based on the image.

    The larger question in this topic starts to delve into whether you can determine if an image that stands alone has been altered or 'faked'. Some are easy, some look fake that are still perpective or lighting tricks that are actually real. There's also the issue of the old optical illusion issue such as things introduced via a lens (anamorphic and astigmatic distortions to name a couple) or just simple perspective arrangements (some of which was employed in the Lord of The Rings to alter sizes of relative characters). These are not by 'provable' from a single image. The analyzer may have to two or more comparative samples, at least one, to demonstrate the 'trick'.

    The JPEG format DOES produce some known patterning when it encounters certain types of alterations (there are some documented color patterns when it see a certain resizing result for instance).

    This is one of the final nails in the coffin for film. As it currently stand a digital fake is generally easier to detect from an 'image'. The idea is that one will be able to produce something like six-sigma certainty for any image printed or virtual. It's coming soon. Or thats the theory.

    A couple of small problems, some of these 'verifications' take teraflops of processor power, per image, per scheme. Size of the image isn't alone the issue. It's how much data you need to compare vs what is being sampled and analyzed. Fun Stuff.

    Like the public key encryption companies, this is a great investment opportunity somewhere down the road. After all, I want to make sure the digital images I see in ten years on Television are real, don't I??
    CDPrice 'drg'
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