What methods are used for digital watermarking? (Choose all that apply.)
a. Implanted subroutines that link to a central Web server automatically when the watermarked file is accessed
b. Invisible modification of the LSBs in the file
c. Layering visible symbols on top of the image
d. Using a hex editor to alter the image data
The correct answer and explanation is :
Correct Answers:
b. Invisible modification of the LSBs in the file
c. Layering visible symbols on top of the image
Explanation:
Digital watermarking is a technique used to embed hidden or visible information within a digital file (such as an image, video, or audio) to protect copyright, authenticate ownership, or detect tampering. The two commonly used methods for digital watermarking include:
- Least Significant Bit (LSB) Modification (Invisible Watermarking) – Option B
- This method modifies the least significant bits (LSBs) of the pixel values in an image.
- Since human vision is not sensitive to minor color changes in individual pixels, altering these bits does not visibly affect the image.
- This watermarking technique is widely used because it ensures that the watermark remains hidden but can still be detected using special extraction methods.
- Layering Visible Symbols on the Image (Visible Watermarking) – Option C
- This involves adding a visible watermark, such as a logo, text, or symbol, over the image to indicate ownership.
- It is commonly seen in stock photos, where the watermark ensures unauthorized usage is discouraged.
- While effective for protection, visible watermarking can sometimes be removed through editing.
Incorrect Answers:
- Option A (Implanted subroutines linking to a Web server)
- This does not qualify as digital watermarking. Instead, it describes a tracking mechanism rather than an embedding method.
- Option D (Using a hex editor to alter image data)
- A hex editor can be used for modifying data, but it is not a watermarking method. Watermarking techniques follow systematic and reversible patterns for detection and verification.
