Digital watermarking is about hiding a small amount of secret data in the content of the host media for various digital forensic and multimedia security purposes. Common applications are:
- Copyright protection, including identification of ownership and buyers
- Content integrity verification and authentication
- Copy control
The figures above are a good example of content integrity verification. The red lights in watermarked images (the upper-right figure) have been replaced with green ones and a pedestrian has been added (the lower-left figure). The tampering is detected when the verifier fails to extracted the original watermark from the tamper areas (see the figure at lower-right corner).