What would be an example of a digital watermark and why?

Question

Thanks! It seems like you know a lot about copyright? I'm in a copyright class and we have to give examples of various copyright words/definitions. I understand the definitions..I just have a hard time coming up with examples...if that makes sense?

Answer 1

I'll answer "why?" first. I'm not sure what you mean, but the purpose is usually to prevent and/or detect copyright violations. Another, related, reason is to make the image unusable (as say a stock photo) but still allow it to be viewed in a way where it's content can be seen. This applies to visible watermarks only and the application I see frequently is people selling images on the web. They want to show their catalogs, but in a way where the digital images can't be simply downloaded from those catalog pages.

EXAMPLES:
I put several links under "Sources" below. These all discuss digital watermarking technology, different ways of doing it and so on and they all have sample images with the various types.

Three types I'm aware of are:

(1) Visible: a visible, (but usually transparent) pattern similar in appearance to the original (non-digital) watermarks.

(2) Invisible: Insert a binary (2-level) pattern into the least-significant bits of the image pixels.

(3) Invisible: Insert a pattern into the image's frequency spectrum. This is the most complicated and the most difficult to detect and remove. To do this: (a) a Fourier transform of the image is computed, (b) a pattern is inserted into that Fourier transform and (c) the inverse Fourier transform is computed. The result is the new, watermarked image, which is visually indistinguishable from the original. The way to detect this is obviously Fourier transforming the image and looking for any obvious patterns. Removing these watermarks is more problematic.

Answer 2

A PGP encrypted signature in a certified email is an example of a digital water mark. It's purpose is for authentication.

Answer 3

It is an icon or signature mark that is sometimes transparent or even invisiable to the naked eye, this can be used for authenticity or security purposes.