Chapter 5: Watermarking

In the traditional manufacture of paper, wet fiber is subjected to high pressure to expel the moisture. If the press' mold has a slight pattern, this pattern leaves an imprint, a watermark, in the paper, best viewed under transmitted light. Now the old word "watermark" has been borrowed by high technology. Digital watermarks are imperceptible or barely perceptible transformations of digital data; often the digital data set is a digital multimedia object. While digital images are most often mentioned in the same breath as digital watermarking, we note that watermarks can be applied to other forms of digital data, for example, videos and music.

History

The watermark first made its appearance in handmade paper over 700 years ago. After the invention of the watermark, its use quickly spread through Italy and then all through Europe. It was primarily used to distinguish one paper manufacturer from another.

Watermarking is related to steganography, but is used in a different context and in a different mindset. Both watermarking and steganography are used to hide information or move information in a cover medium, but after this they begin to differ.

Steganography:

• Is not robust or has limited robustness

• Tries to hide the fact that there is hidden information

Watermarking:

• Is designed to be robust

• While not always visible, is designed to carry hidden information

With the explosion of digital art and media available, it is no surprise that digital watermarking has gained a great deal of attention since about 1995. At that time only 13 publications about digital watermarking existed; that number jumped to 103 three years later.