Image Processing Reference
In-Depth Information
hundreds of thousands of illegal DVD disks and that they are culpable and liable for mil-
lions of dollars of lost revenue.
To accomplish this, visible and invisible encoding techniques must be used for the
identifying codes, including data values inserted directly into the stream. Techniques such
as hiding information in what looks like film grain or dust particles on a film print may
also be used, and if this becomes known, then changing the audio or removing and adding
frames to the edited movie might also be used to differentiate one copy from another.
Subtly shifting the subtitles to a new time code might be sufficient to encode some values.
Comparing them against the master might then yield the coded information. If enough
different techniques are used, there should still be some trace of the transaction ID left
even after the video has been duplicated and passed on several times.
Problems With Artifacts
One of the issues with watermarking is that it must be robust enough to survive the video
content being reformatted and compressed.
Watermarking is very similar to the technique known as steganography, which hides
data within the complexity of the picture information. Hidden messages are encoded into
images and can be extracted if the key or cipher is known.
This is very similar to the code based on a series of holes cut in card, which is then
placed over the correct page of a book so that the message can be read.
Steganography just hides a message somewhere in an image. Watermarking must be
hard to remove but must also be invisible. This is easy to do with a still image and much
harder to do with a moving image. The watermark becomes visible occasionally because it
appears to be a stationary noise pattern while the rest of the underlying image is moving.
During 2002-03, the BBC Research and Development laboratories demonstrated
motion-tracked watermarks that were designed to move with the video. The difference
when viewing watermarked video with a slow pan was remarkable—the watermark was
much harder to detect. This technique is somewhat related to the motion detection and
compensation in the video-compression systems.
Hiding codes and watermarking information in the deeper recesses of the compres-
sion data may be another useful technique. In addition, many other techniques are avail-
able to hide unique identifying codes in movies.
Patent Pools and Technology Licenses
You must be diligent in determining whether or not you have to pay a license to use some
footage. Even if you are simply providing a compression service, there may be some
licensing issues to deal with.
You should consult the licensing terms for the encoder you are using if you think
there is an issue. Older encoders such as MPEG-2 probably have all the licensing embod-
ied in the purchase of the encoder software and hardware. The manufacturer pays a por-
tion of the sales price as a levy.
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