Contents What is DWM ? Applications Classification Working Attacks Advantages and Disadvantages Techniques
Digital Watermarking We add ‘Visible’ or ‘Invisible’ structure called ‘Watermarks’ to digital media. The process of adding watermarks is called ‘Digital Watermarking’. Adaptation of Paper Watermarks. Describes methods and technologies that allow to hide/embed various types of information to digital document. In general Digital Watermarking means “Author Signature”.
Classification Perceptible Watermarks and Imperceptible Watermarks Robust Watermarks and Fragile Watermarks Private Watermarks and Public Watermarks
Classification (contd.) Perceptible Watermarks and Imperceptible Watermarks Perceptible Watermarks are visible to human eye Useful for primary Applications. E.g. of watermark in a video E.g.. Of watermark in a image Imperceptible watermarks are Invisible to human eye. Used in the places where the content being watermarked must appear in unchanged form. Remains hidden in content and can be detected only by authorized agencies.
Classification (contd.) Robust Watermarks and Fragile Watermarks Degree to which watermarks can withstand any modification of any type (Accidental or Intentional ). Robust Watermarks are difficult to remove from the object in which they are embedded. Perceptible Watermarks are more Robust. Fragile Watermarks can be easily destroyed by any attempt to temper with them.
Classification (contd.) Private Watermarks and Public Watermarks Private Watermark requires at least original data to recover watermark. They are also known as ‘Secure Watermarks’. Public Watermark requires neither original data nor embedded watermark to recover watermark information.
Working Typical DWM system consists of mainly 3 parts / process Watermark Insertion Watermark Extraction Watermark Detection
A Generic Watermarking System Cover Work Watermarked Detected Watermark Watermark Watermark Embedder Work Detector MessageWatermark Message
User Key Watermarked Input Image Watermark Insertion Image Watermark User Key Extracted Watermark Extraction Watermarked Watermark Image User KeyWatermarked Decision Watermark Detection Image ( Yes or No ) Specified ID ( Watermark )
General Digital Watermarking Process(a) Watermark Embedding Digital Watermark 0101 …. . . .. . . Original Data Watermarked Data Embedding Algorithm 0101 …. . Distribution
General Digital Watermarking Process (contd.)(b) Watermark Extraction Original DataWatermarked Data Extracted Watermark Extraction 0101 …. . 0101 …. . . .. . . Algorithm
Attacks (contd.) Geometric Attack Subtractive Attack involves ‘removing’ the mark by cropping or digital editing. Distortive Attack attempts to make some ‘uniform distortive changes’ in the image such that mark becomes ‘unrecognizable’.
Attacks (contd.) Forgery Attack Also known as ‘Additive Attack’. The attacker include his/her own watermark overlaying the original image and marking the content as their own.
Advantages Uniquely identifies the author of copyrighted work. Implementation on PC platform is possible. Embedding watermark is easy Image Tampering Detection
Disadvantages Watermarking doesn’t prevent image copying but we can track down and detect ownership of copied images. Watermarks vanishes if someone manipulates the image. Resizing, compressing images from one file type to another may diminish the watermark and it becomes unreadable.
DWM Techniques Image Domain Encoding Also known as Least Significant Bit (LSB). LSB works by reducing the no of colors used by image itself and uses the rest of the palette to encode the information. If the colors in an image are less then more information can be stored without quality loss.