Digital Watermarking

Which brings us to MPEG-21, our multimedia umbrella standard. There is no point in
using a compressed digital image in court if it is not admissible evidence. Digital
images can be challenged on the basis that they may have been altered between point
of capture (the video surveillance device) and point of presentation (the court).

MPEG-4 started to address the codification of ownership rights and proof of
ownership and proof of provenance. The technique is sometimes known as digital
watermarking—the digital countersigning of an image such that it can be demonstrated
that the image was produced by a specific person or device and has not been altered
prior to or during storage or delivery, that is, the whole process of authentication.
Digital watermarking can be used to provide an audit trail showing the path an image
has taken and what has happened to the image.
You must be careful that the compression used does not destroy the digital
watermark; it is always a good idea to compress and then watermark a digital image
data stream.