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Is there a watermarking technique which doesn't make the watermark obvious yet by analyzing the image you can identify the source?

hakre
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Muhammad Hasan Khan
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  • Is this for images or other types of signals? – Phonon Apr 06 '11 at 13:06
  • Related: [How can you hide information inside a jpg or gif photo?](http://stackoverflow.com/questions/1216156/how-can-you-hide-information-inside-a-jpg-or-gif-photo) – hakre Apr 05 '13 at 02:25

3 Answers3

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Yes, it's called "robust" digital watermarking (of images). A robust digital watermark should be recognizable even when you compress, resize, crop or translate the image. Because you can't embed robust digital watermarks into lowest-order bits, say (as they get lost in compression), the process is typically

  1. transform the image to an alternative space, e.g. using discrete cosine transform
  2. embed the watermark in the transformed space
  3. transform the compound result back to the original space, e.g. reverse discrete cosine transform

BTW in order to make the watermark non-obvious but recognizable, you just need to make sure that the watermark in itself is random so that you can't immediately recognize it even if you carry out the watermark extraction procedure if you don't know that the watermark should be.

Antti Huima
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This is my implementation: https://www.facebook.com/ChromaShift/

It is not as good as Digimarc Barcode but works well and can be integrated into web apps for dynamic "stegging" of JPEGs. There is a fairly detailed white paper and manual (pdf) document on the page.

Fotios Basagiannis
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Perhaps you could employ steganographic tehniques to hide a signature in the lower-order bits of the image?

(Edit: A disadvantage of steganography is that any resizing, reencoding or format change of the picture is likely going to destroy the information.)

Aasmund Eldhuset
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