Data hiding is the general process by which a discrete information stream, the mark, is merged within media content by imposing imperceptible changes on the original host signal. Other requirements, other than transparency, can be needed according to the speciﬁc application that is taken into account. When these techniques are used to preserve the copyright ownership with the purpose of avoiding unauthorized data duplications, the embedded watermark should be detectable. This is required even if malicious attacks or non-deliberate modifications (i.e., filtering, compression, etc.) affect the embedded watermark. This requirement is known as watermark security. Capacity is another watermarking requirement, referring to the number of bits of information that can be embedded in the original data, which needs to be fulfilled, depending on the specific application. These requirements conflict each other. Therefore the optimal trade-off is strictly tied to the target application.
In the past decades, there has been an explosion in the use and distribution of digital multimedia data, essentially driven by the diffusion of the Internet. In this scenario, data hiding techniques have been devised to answer the ever-growing need to protect the intellectual property (copyright) of digital still images, video sequences, or audio from piracy attacks in a networked environment like the World Wide Web. Although copyright protection was the driving force for the development of data hiding techniques, different uses have been proposed in literature. Fingerprinting, copy control, broadcast monitoring, data authentication, multimedia indexing, content-based retrieval applications, medical imaging applications, covert communication (steganography), and error concealment, are only a few of the new applications where watermarking can be usefully employed. Moreover, data hiding has been recently used for quality assessment purposes, as well as for improved data compression.
Within this framework, our research activity has been devoted to:
- Perceptual aspects in data hiding,
- Image watermarking for improved image coding,
- Watermarking for blind channel quality assessment,
- Watermarking for copyright protection for:
- 2D images,
- High Dynamic Range (HDR) images,
- stereo images,
- video sequences.