INTRODUCTION
WATERMARKING is the process
that embeds data called a watermark, a tag, or label into a multimedia
object such that the watermark can be detected or extracted later to
make an assertion about the object. The object may be an image, audio,
video, or text. Whether the host data is in spatial domain, discrete
cosine-transformed, or wavelet-transformed, watermarks of varying degree
of visibility are added to present media as a guarantee of
authenticity, ownership, source, and copyright protection. In general,
any watermarking scheme (algorithm) consists of three parts, such as the
following:
1) watermark;
2) encoder (insertion algorithm);
3) decoder and comparator (verification or extraction or detection algorithm)
Whether each owner has a unique
watermark or an owner wants to use different watermarks in different
objects, the marking algorithm incorporates the watermark into the
object. The verification algorithm authenticates the object determining
both the owner and the integrity of the object. Watermarks and
watermarking techniques can be divided into various categories. The
watermarks can be applied either in spatial domain or in frequency
domain. It has been pointed out that the frequency-domain methods are
more robust than the spatial-domain techniques. On the other hand, the
spatial domain watermarking schemes have less computational overhead
compared with frequency-domain schemes. According to human perception,
the digital watermarks can be divided into four categories:
1) visible;
2) invisible-robust;
3) invisible-fragile;
4) dual.
A visible watermark is a
secondary translucent image overlaid into the primary image and appears
visible to a casual viewer on careful inspection. The invisible-robust
watermark is embedded in such a way that modifications made to the pixel
value is perceptually not noticed, and it can be recovered only with
appropriate decoding mechanism. The invisible-fragile watermark is
embedded in such a way that any manipulation or modification of the
image would alter or destroy the watermark. A dual watermark is a
combination of a visible and an invisible watermark. In this type of
watermark, an invisible watermark is used as a back-up for the visible
watermark.
VIDEO DEMO
http://www.youtube.com/watch?feature=player_embedded&v=ik-HUJckMLo
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