Digital watermarks are invisible or visible marks on an electronic image, music, video, text, or any material that serve the purpose of protecting the copyright of a material’s owner. In this sense, digital watermarks are like the watermarks used in currencies for counterfeit security. Stenography can also be applied in digital watermarks if one wants to make the watermark less detectable.

A digital watermark is primarily a transparent image overlaid on the actual image. In some cases, though, digital watermarks cannot be detected by the human eye and includes important information about the owner such as the name and the date.

Visible Watermarks

Visible watermarks change the original media in such a way that the new signal can easily be differentiated from the original one. This is so that the copyright is easily visible and enforceable. Using the image, video or document for purposes without the consent of the owner would then result in a lower resolution image or video.

Visible watermarks can also serve to advertise a website, or the company or person from which the original image, document or video came from. In this way, visible watermarks can also serve as advertising or marketing tools.

Invisible Watermarks

Invisible watermarks, on the other hand, do not restrict the use of the images, videos or documents nor do they alter the quality of these materials in any significant way. Invisible watermarks are used to track the images, documents or videos to its original owner.

Tracking illegitimate copies of copywrited material using invisible watermarks is a process called fingerprinting. Fingerprinting makes it easier for authorities to track down violators because the pirates’ personal or system information is included along with the copyright information in the copied materials.

Whether visible or invisible, digital watermarks can be circumvented through cropping or zooming techniques. Digital watermarks created through special techniques are especially susceptible to this, unlike mixed domain and frequency domain techniques.

Digital Watermarks in Documents and Text

Digital watermarking texts and sensitive documents is a lot more difficult than watermarking images and videos. There are a lot of redundancies in images, music files and videos. Since every pixel carries with it information, watermarking these types of media is a lot easier than doing the same on sensitive documents or text where every letter or word is important.

University research professors in Purdue have suggested a way of effectively imprinting a digital watermark in texts by using the structure or the syntax of the language itself to embed the watermark. By using a special algorithm, digital watermarks can be contained within a text or a document by making small grammatical changes in the document while keeping the meaning the same. Moreover, this technique has been found to be effective even when some words have been deleted or changed from the document.

With the growing threat of piracy in the Internet and copyright infringement cases, digital watermarks are sure to serve an important role in the future of intellectual property protection.