Besides applications in the fields of copyright protection, authentication and security, digital watermarks can also serve as invisible labels and content links. For example, photo development laboratories may insert a watermark into the picture to link the print to its negative. To find the negative for a given print, simply scan the print and extract the information about the negative. In another scenario, digital watermarks may also be used as a geometrical reference, which may be useful for programs such as optical character recognition (OCR) software. The embedded calibration watermark may improve the detection reliability of the OCR software since it allows the determination of translation, rotation, and scaling.
The three pictures below illustrate this application. Image (a) shows an original photo of a car that has been protected with a watermarking technology. In photo (b), the same picture is shown, but with a small modification: the numbers on the license plate have been changed. Image (c) shows the photo after running the digital watermark detection program on the tampered photo. The tampered areas are indicated in white. We can clearly see that the detected area corresponds to the modifications applied to the original photo.
Digital Watermarking describes methods and technologies that hide information, for example a number or text, in digital media, such as images, video or audio. The embedding takes place by manipulating the content of the digital data, which means the information is not embedded in the frame around the data. The hiding process has to be such that the modifications of the media are imperceptible. For images, this means that the modifications of the pixel values have to be invisible. Furthermore, the watermark must be either robust or fragile, depending on the application. By "robust", we mean the capability of the watermark to resist manipulations of the media, such as lossy compression (where compressing data and then decompressing it retrieves data that may well be different from the original, but is close enough to be useful in some way), scaling, and cropping, among others. In some cases, the watermark may need to be fragile. "Fragile" means that the watermark should not resist tampering, or would resist only up to a certain, predetermined extent.
The example below illustrates how digital watermarking can hide information in a totally invisible way. The original image is on the left; the watermarked image is on the right and contains the name of the author.
Digital video watermarking can be achieved by either applying still image technology to each film frame or using dedicated methods that exploit inherent features of the video sequence. For more information, click .
The first applications that came to mind were related to copyright protection of digital media. In the past, duplicating artwork was quite complicated and required a high level of expertise for the counterfeit to look like the original. However, in the digital world, this is not true. Today, it is possible for almost anyone to duplicate or manipulate digital data, while not losing data quality. Similar to a painter's signature or monogram, today's artists can copyright their work by hiding their name within the image. Hence, the embedded watermark allows identification of the owner of the work. It is clear that this concept is also applicable to other media, such as digital video and audio. Currently, the unauthorized distribution of digital audio and video over the Internet is a big problem. In this scenario, digital watermarking may be useful to set up controlled audio distribution and to provide efficient means for copyright protection, usually in collaboration with international registration bodies.
There are a number of possible applications for digital watermarking technologies and this number is increasing rapidly. For example, in the field of data security, watermarks may be used for certification, authentication, and conditional access. Certification is an important issue for official documents, such as identity cards or passports.
That means that key information is written twice on the document. For instance, the name of a passport owner is normally printed in clear text. But it would also be hidden as an invisible watermark in the passport photo. If anyone tries to tamper with the passport by replacing the photo, it would be possible to detect the change by scanning the passport and verifying the name hidden in the photo.
An exhaustive list of digital watermarking applications is of course impossible. However, it is interesting to note the increasing interest in fragile watermarking technologies. Especially promising are applications related to copy protection of printed media. Examples here include the protection of bills with digital watermarks. Various companies have projects in this direction and it is very likely that fully functioning solutions will soon be available.