Table 3.

Watermarking Approaches

Technique	Definition	Application
Visible watermark	It is mainly a semi-transparent text or image embedded in the cover image.	Logo on TV channel
Invisible watermark	The watermark is embedded to be invisible to the user’s naked eye, but it can easily be identified that the image is watermarked or not by the computer devices.	Copyright protection applications
Robust watermarking	Robust watermarking techniques are resistant to multiple various attacks. The authors in [125] applied the SVD method to the medical image watermarking technique based on FDCuT-DCT. The proposed algorithm has good imperceptibility so that it can maintain the quality of medical images	used in copyright protection
Fragile watermarking	Watermark allows being demolished by straightforward alteration easily. Any slight change in the watermarked image will cause the watermark to break, low imperceptibility	integrity verification, and authentication applications.
Semi-fragile watermarking	Defend on the covered data against deliberate attacks but is frail against malignant attacks.	Copyright protection but with Low imperceptibility
Zero watermarking	Unlike other watermarking techniques, the watermarking process does not modify the image, as the watermark does not embed in the image itself [141].	Copyright protection, authentication, and tamper detection for medical data
Hybrid watermarking	It is a combination of robust and fragile techniques	Integrity verification, copyright protection, and authentication concurrently.