Digital watermarking

A digital watermark is a kind of marker covertly embedded in a noise-tolerant signal such as audio, video or image data.

Digital watermarks may be used to verify the authenticity or integrity of the carrier signal or to show the identity of its owners.

[3] If a digital watermark distorts the carrier signal in a way that it becomes easily perceivable, it may be considered less effective depending on its purpose.

For marking media files with copyright information, a digital watermark has to be rather robust against modifications that can be applied to the carrier signal.

Both steganography and digital watermarking employ steganographic techniques to embed data covertly in noisy signals.

While steganography aims for imperceptibility to human senses, digital watermarking tries to control the robustness as top priority.

The first successful embedding and extraction of a steganographic spread spectrum watermark was demonstrated in 1993 by Andrew Tirkel, Gerard Rankin, Ron Van Schyndel, Charles Osborne, and others.

There are many possible modifications, for example, lossy compression of the data (in which resolution is diminished), cropping an image or video, or intentionally adding noise.

On videos and images, some are made transparent/translucent for convenience for consumers due to the fact that they block portion of the view; therefore degrading it.

Spread-spectrum watermarks are known to be modestly robust, but also to have a low information capacity due to host interference.

Quantization watermarks suffer from low robustness, but have a high information capacity due to rejection of host interference.

Both cameras added irremovable features to the pictures which distorted the original image, making them unacceptable for some applications such as forensic evidence in court.

[9] A secure digital camera (SDC) was proposed by Saraju Mohanty, et al. in 2003 and published in January 2004.

[10] Blythe and Fridrich also have worked on SDC in 2004 [9] for a digital camera that would use lossless watermarking to embed a biometric identifier together with a cryptographic hash.

A survey of the current state-of-the-art and a classification of the different techniques according to their intent, the way they express the watermark, the cover type, granularity level, and verifiability was published in 2010 by Halder et al. in the Journal of Universal Computer Science.