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Invisible Watermarks as Digital Signatures Disclosure Number: IPCOM000031559D
Original Publication Date: 2004-Sep-29
Included in the Prior Art Database: 2004-Sep-29
Document File: 1 page(s) / 29K

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Digital images are easily traded on the internet with or without the authors consent. Watermarks help to prove the ownership of an image. However, people who have bought an image don't want to see the watermark and so was born the need for invisible watermarks. Described is a method of placing truly hidden watermarks within an image that can't be removed in any easy manner.

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Invisible Watermarks as Digital Signatures

The owner of the image would use a specially designed image editor that can place the owners designed watermark anywhere on the image. The watermark may be a text string or artist signature or logo.

Pixels that are overlaid by the watermark reference a small set of color registers. The affected pixels are mapped to a new set of color registers which contain the same color values as the original set. These new color registers are added to the color palette of the image and the image is saved.

The image editor knows that the last N registers are the watermark registers and so sets them to a fixed color or intensity to show the watermark.

Ordinary viewing of the image will show no watermark, but viewing it with the special image editor will show the watermark. Watermark registers within the palette is a manner controlled by the image key.

For tighter security, the owner may provide an image key when adding the watermark which will be used to shuffle the color registers in the color palette (and adjust the image pixel references as well).

To see the watermark, the owner unlocks the watermark by providing the image key. The image editor then unshuffles the registers and then sets the last N to a fixed color to show the watermark or alternatively the image could be compared to the original image with color value differences shown. The shuffling hides the watermark registers within the color palette making it difficult to remov...