Digitally Signed Photos


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lurgee

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Aug 17, 2003
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#1
Hi all,

Recently saw some photographers stating that their photos are digitally signed. Can anyone explain what it means and how do we go about doing it?

Thanks!
 

Jan 23, 2005
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#4
lurgee said:
Recently saw some photographers stating that their photos are digitally signed. Can anyone explain what it means and how do we go about doing it?
I assume you refer to digital watermarking. This refers to embedding some date into a picture that can be used to identify pictures or track where other (modified) versions of a picture originate from. Digital watermarks could tell a printing service for example that the picture is not licensed for printing. It is also a tool to prove ownership of pictures (assuming that only the owner can provide the opriginal picture with the watermark completely removed). They are one example of DRM (digital rights management) methods.

Digital watermarks are embedded in (more or less) "invisible" ways into the pictures. Some schemes won't affect the image information at all, but those are trivially defeated (e.g. by converting the image file to a different format). Robust watermarks have to survive format conversions as well as transformations such as scaling, rotating, cropping, etc.

Watermarks that don't grossly deteriorate the image are usually easy to remove if the algorithm used is known - one reason why there's a lot of secrecy about commercial solutions. I've got a version of Photoshop Elements that came with a watermark decoder.

Here's one commercial supplier of watermarking systems: http://www.digimarc.com/watermark/
 

lurgee

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LittleWolf said:
I assume you refer to digital watermarking. This refers to embedding some date into a picture that can be used to identify pictures or track where other (modified) versions of a picture originate from. Digital watermarks could tell a printing service for example that the picture is not licensed for printing. It is also a tool to prove ownership of pictures (assuming that only the owner can provide the opriginal picture with the watermark completely removed). They are one example of DRM (digital rights management) methods.

Digital watermarks are embedded in (more or less) "invisible" ways into the pictures. Some schemes won't affect the image information at all, but those are trivially defeated (e.g. by converting the image file to a different format). Robust watermarks have to survive format conversions as well as transformations such as scaling, rotating, cropping, etc.

Watermarks that don't grossly deteriorate the image are usually easy to remove if the algorithm used is known - one reason why there's a lot of secrecy about commercial solutions. I've got a version of Photoshop Elements that came with a watermark decoder.

Here's one commercial supplier of watermarking systems: http://www.digimarc.com/watermark/
thank you for taking the time to explain. i guess that's what they meant by digitally signing their photos. heh.

hmmz..seems like it's not cheap to use the digimarc software.
 

Jan 23, 2005
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#6
lurgee said:
hmmz..seems like it's not cheap to use the digimarc software.
It's IMHO the wrong approach: it is fighting the symptoms of a society problem with technology. Robustness of watermarks is not guaranteed; a while back there was a competition (initiated by the music industry) to break a watermarking scheme for music without any technical specifications what it was based on. It didn't take long for it to be hacked.

Watermarking can be made more robust if one tolerates degradation of the image. E.g, one could crop/mask out completely a portion of a photo; the missing information can only be supplied by the owner of the photograph, proving authenticity. A variant of this is writing your name/copyright information over the imoportant parts of the picture, ruining the image. Whiule popular, this is hardly an acceptable "solution".
 

lurgee

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#7
LittleWolf said:
It's IMHO the wrong approach: it is fighting the symptoms of a society problem with technology. Robustness of watermarks is not guaranteed; a while back there was a competition (initiated by the music industry) to break a watermarking scheme for music without any technical specifications what it was based on. It didn't take long for it to be hacked.

Watermarking can be made more robust if one tolerates degradation of the image. E.g, one could crop/mask out completely a portion of a photo; the missing information can only be supplied by the owner of the photograph, proving authenticity. A variant of this is writing your name/copyright information over the imoportant parts of the picture, ruining the image. Whiule popular, this is hardly an acceptable "solution".
I agree with your last paragraph. :) Most of us just add our signatures on the photo itself, some on the important parts and some just where they deem fit. It's easier too I guess compared to the other method of watermarking it digitally.
 

#8
I think watermarking will not work for screen captures. Unless you add another layer of your own watermark over the image. And also it may still spoilt the look, but if it does cover the image fully as I dun think anyone will want to use that watermarked image.

There are no 100% way of watermarking for sure.:cry: But it will deter people from stealing.:)
 

Jan 23, 2005
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#9
leumas01 said:
There are no 100% way of watermarking for sure.:cry: But it will deter people from stealing.:)
I'm not so sure about that. If someone shows me that s/he doesn't respect/trust me enough to provide me with uncensored/unrestricted information/data, I'm less inclined to respect them and their intellectual property either. If, instead of just locking your door, you install a network of surveillance cameras and infrared detectors and start to search visitors' bags, it probably won't help friendly relations with your neighbours either.

It is also very tempting to try out if/how technological measures can be defeated, even if the picture/music/data would be completely uninteresting/worthless on its own.
 

ortega

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Nov 2, 2004
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#10
i'd rather ppl leech my photos and let me sue them
it is more profitable

remember street directory.com sued some companies $10K for using their maps?
 

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