JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV Year STEGANOGRAPHY AND WATERMARKING Previous Question Paper (September - 2020 - R16)

Digital watermarking is the process of embedding information (the watermark) into a digital signal, such as an image, audio, or video, in a way that is often imperceptible to the human eye or ear. The watermark carries data related to the host signal, such as copyright information, ownership identity, or authentication codes, which can be extracted or detected later to prove ownership or verify integrity.

The generic watermarking system consists of two main processes: the Embedding Process and the Extraction/Detection Process.

• Embedding: The original host signal and the watermark signal are passed through an embedder. A secret key is often used to ensure security. The output is the watermarked signal, which is transmitted or stored.
• Extraction/Detection: The received (possibly corrupted) signal is processed. If the system uses a secret key, it is provided to the detector to retrieve the watermark or verify its presence.

The system architecture can be visualized as a flow where the host signal and watermark input meet at the encoder (embedder) using a key, resulting in the watermarked content. At the receiver, the watermarked content is processed by the decoder (detector) using the same key to recover the watermark or a binary decision indicating its presence.

The watermark embedder is the functional unit responsible for inserting the watermark signal into the host data. Its primary functions include:

1. Data Integration: It combines the host signal and the watermark signal using a specific algorithm (such as LSB insertion, spread spectrum, or transform domain techniques).
2. Security Enforcement: It incorporates a secret key to ensure that only authorized parties can embed or later detect the watermark, preventing unauthorized removal or tampering.
3. Perceptual Control: It ensures that the watermark is embedded such that it remains imperceptible to the observer, maintaining the quality and fidelity of the original host signal.
4. Robustness Optimization: It structures the watermark data to survive common signal processing operations, such as compression, cropping, or filtering, depending on the application requirements.