24 Oct
2011
24 Oct
'11
4:10 a.m.
No it is not. All a watermark does it to identify the source
of the data it is embedded in, and in such a way that can't be
removed easily. That does not imply any use of it.
Hmm... it seems to me that if the watermark does not cause audible
distortion, then shouldn't there be a simple algorithm to remove the
watermark: namely, to watermark the same file again with different
information?
I suppose this requires you to know the algorithm used to watermark the file
in the first place. All the algorithms discussed here:
http://www.ece.uvic.ca/~aupward/w/watermarking.htm seem like they would be
pretty trivially removed by the applying them again with different watermark
data.
I could imagine that one could choose from different frequency bands, and
hide the data in only one of them, so that in order to remove it you'd need
to know which band it's in, or over-write the data in *all* bands. But in
order to make the ratio of noise generated by watermark-all-bands vs
watermark-one-band large enough that watermarking all bands would introduce
unreasonable noise, but just watermarking one wouldn't, it seems the bands
would have to be very small. How much data could you really fit in them
(and what are the chances that any one of the bands happens to look
"watermarked" with something meaningful)?
But perhaps there is some other way to parametrize the algorithm so that if
the parameters are not equal, the watermarks can coexist. I would be
interested in seeing it. But my feeling is that the amount of data you can
robustly store is small enough that splitting it into a reasonable number of
bands to thwart removers would make the capacity unreasonably small.
Jeremy