Watermarks: Protecting the image
With images widely available on the Internet, it may sometimes be
desirable to use watermarks. A watermark is a secondary image which is
overlaid on the primary image, and provides a means of protecting
the image.
Visible watermarks
A visible watermark is a visible translucent image which is overlaid on
the primary image. Perhaps consisting of the logo or seal of the
organization which holds the rights to the primary image, it allows the
primary image to be viewed, but still marks it clearly as the property
of the owning organization.
It is important to overlay the watermark in a way which makes it
difficult to remove, if the goal of indicating property rights is to be
achieved.
An example shows both a watermark and an
image with the watermark overlaid.
Invisible watermarks
An invisible watermark is an overlaid image which cannot be
seen, but which can be detected algorithmically. Different
applications of this technology call for two very different types of
invisible watermarks:
- A watermark which is destroyed when the image is manipulated
digitally in any way may be useful in proving authenticity of an
image. If the watermark is still intact, then the image has not been
"doctored." If the watermark has been destroyed, then the image has
been tampered with. Such a technology might be important, for example,
in admitting digital images as evidence in court.
- An invisible watermark which is very resistant to destruction
under any image manipulation might be useful in verifying ownership of
an image suspected of misappropriation. Digital detection of the
watermark would indicate the source of the image.
Here is a sample split image with the upper right half invisibly watermarked
and the lower left half unwatermarked.
The upper pattern is the watermark detection from the upper right image;
the lower pattern is the watermark detected from the lower left unwatermarked image.
[
Image applications home ]
