About Digital Watermarking

Digital watermarking technologies allow users to embed into audio, video, still images and printed documents a digital code that is imperceptible during normal use but readable by computers and software.  The major purpose of digital watermarks is to provide protection for intellectual property that is in digital format. In this process, also referred to as data embedding, information hiding, steganography, or simply watermarking, a pattern of bits is inserted into a digital image, audio or video file that identifies the file's ownership and can convey additional information such as copyright (author, rights, etc.). The name comes from the faintly visible watermarks imprinted on stationery that identify the manufacturer of the stationery.

Unlike printed watermarks, which are intended to be somewhat visible, digital watermarks are designed to be completely invisible, or in the case of audio clips, inaudible. Moreover, the actual bits representing the watermark must be scattered throughout the file in such a way that they cannot be identified and manipulated. And finally, the digital watermark must be robust enough so that it can withstand normal changes to the file, such as rotation, filtering or the application of compression algorithms such as JPEG that discard some of the original data (lossy compression).

Satisfying all these requirements is no easy feat, but there are a number of companies offering competing technologies. All of them work by making the watermark appear as noise - that is, random data that exists in most digital files anyway. To embed or view a watermark, you need special programs provided by a specific company that know how to process that company’s watermark data. Resources for watermarking in a variety of media include Blue Spike Inc. (www.bluespike.com), Digimarc Corp. (www.digimarc.com), Macrovision Corp. (www.macrovision.com, MediaSec Technologies LLC. (www.mediasec.com/html/en/index.htm), Signum Technologies (www.signumtech.com), and Verance (www.verance.com).

An example of the effect of watermarking on a digital image:

Digimarc Watermarking

Digimarc Corp. has developed watermarking technology for digital and printed images and for digital and analog video and audio.  Specialized software embeds these "imperceptible" messages by making subtle changes to the data of the original digital content. These watermarks can then be "read" to validate original content and/or deliver an action, such as delivering content to a mobile phone or providing contact information about the owner of an image.

The changes to the media are so subtle that Digimarc digital watermarks are considered imperceptible.  To help illustrate the impact of a digital watermark, here is a comparison of an original image, a digitally watermarked image, and the result of an image calculation done through a Digimarc-enabled application. The image calculation allows you to see the changes to the image caused by embedding the digital watermark. The calculation is created by subtracting the original image from the watermarked image; the result is then exaggerated for illustration purposes.

Using Digimarc Watermarking

Digital watermarking requires both a method for embedding the watermark into a digital file and a method for reading an embedded watermark.  The technology developed by Digimarc Corp. for watermarking still images has been incorporated into plug-ins that are provided with Adobe Photoshop Elements (watermark reader) and Adobe Photoshop (watermark embedder and reader).   The plug-ins can be accessed from the menu bar by selecting Filter>Digimarc>Embed Watermark or Filter>Digimarc>Read Watermark.  Plug-ins are also available for other image processing applications. Digimarc also supplies a stand-alone watermark reader that can identify watermarked images in Windows Explorer and Internet Explorer on PC platforms.  Finally, a Software Development Kit (SDK) allows programmers to integrate watermarking into database, asset management or other software applications.

The following information can be embedded in an image:

Digimarc provides for-fee services related to watermarking, including:

Watermarks can be embedded in any file format supported by Photoshop, including TIFF, PICT, JPEG, GIF, PNG, PSD, and BMP.  In general watermarks survive conversion from one format to another and from one color mode (RGB, Grayscale) to another.  Watermarks are most effective when applied to images that contain some degree of variation or randomness.  The white areas in the right-hand bridge image above represent the flat areas of the original image where watermarking intensity is decreased to avoid distortion.  A minimum image size of 256x256 pixels is recommended for robust watermarking, especially if an image is to be compressed, cropped or rotated before its actual use.  There is no upper size limit.  In general, watermarking should be the last operation performed on an image.

The recommended workflow for embedding a watermark is as follows:

Created by: Cheryl Cramer

Last update: May 11, 2005