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1. What is digital watermarking?

Digital watermarking is the process of embedding copyright information or restrictions into a digital object of some kind, such as an image or audio file.

There are two forms a digital watermark can take: invisible and visible. Visible watermarks generally consist of discretely applied logos designed to communicate ownership, while at the same time not obscuring the image itself. Photo editing software such as Photoshop, for example, can be used for this purpose. The advantage of including visible watermarks on images is that they provide users with immediate notification of copyright. The disadvantage of relying on visible watermarks alone is that they can be detected and -- with enough editing -- removed.

In contrast, the goal of invisible watermarking is to embed identification information in such a way as to make its alteration or removal as difficult as possible. The two main parts of this method include: firstly, using watermark embedding software to apply the watermark to images you want to protect; and secondly, upon discovery of an image suspected of copyright violation, using watermark reader software to recover the identification information. A combination of visible and invisible methods is often used, although the visible mark may also serve to announce to the malicious hacker that the image has an invisible mark as well.

2. Why would you want to digitally watermark images?

The whole point of digital watermarking is to provide a method for marking digital assets with copyright information in a way that later enables one to produce compelling evidence of ownership in legal disputes where ownership of such assets have been put in question. This implies, of course, that individuals or organizations applying a watermark to an image actually have copyright of the original image.

3. How does digital watermarking work?

A digital watermark is created by converting an owner's specified copyright information into slight changes in the image that are encoded and imperceptibly distributed across the image. The encoded information can then be retrieved and displayed by watermark reading software. There are a variety of embedding techniques used by different vendors, for example, the "Patchwork" algorithm, texture block coding, private key cryptography, etc.; but all of them are designed to hide copyright information that can be recovered and used to identify the original owner of the image.

4. How do you watermark an image?

This depends on the software used to create the watermark. Software such as Digimarc's PictureMarc and Signum's SureSign now come as a free plug-ins for popular photo editing packages like Photoshop. Digimarc offers instructions on how to apply watermarks using various photo editing packages. Most of these products also offer standalone software that includes the ability to batch process a collection of images. In addition, most watermarking vendors maintain a registry database for purposes of validating ownership. Typically, there are license fees associated with the watermarking and registry services. One other service that many companies are now providing is a web spider service designed to comb the web looking for possible violations of copyright of a given customer's registered images. This service is typically an option that would involve an additional service fee.

5. How effective is watermarking?

Virtually no technique for protecting digital assets is inpregnable to attacks from determined hackers. Watermarking is no different. There are "watermark cracking" programs and many other methods of defeating watermark schemes. At the same time, watermarking does provide at least an initial line of defense against copyright abuses. A University of Edinburgh report provides more information about the weaknesses of various watermarking schemes.

6. What are some of the major vendors of watermarking software?

The links below are provided as a starting point for those interested in finding information about some of the primary vendors of watermarking software. No endorsement of these vendors is intended or implied.

·  Digimarc

http://www.digimarc.com/index.shtml

·  Alpha-Tec (EIKONAmark)

http://www.alphatecltd.com/

·  Giovanni

http://www.bluespike.com/giovanni.html

·  Signum Technologies

http://www.signumtech.com/docs/index.html

·  MediaSec (SysCoP)

http://www.mediasec.com/products/index.html

7. Are there places on the web where I can go to find more information about digital watermarking?

Yes. These include:

·  Creating and Using Watermarks.

http://desktoppub.about.com/compute/desktoppub/cs/watermarks/

·  Digital watermarking: perfecting the art of security.

http://www.spie.org/web/oer/november/nov99/cover1.html

·  Digital Watermarks: New Tools for Copyright Owners and Webmasters.

http://www.webref.com/content/watermarks/

·  Protecting Your Images with Digital Watermarks.

http://webreview.com/pub/98/01/09/addict/

·  A Survey of Digital Watermarking.

http://www.cc.gatech.edu/~mjm/dw/watermarking.html

·  Watermarks.

http://www.webreference.com/multimedia/watermarks.html

How to Participate