Digital Watermarking Sapinkumar Amin Guided By: Richard Sinn

Agenda What is Digital Watermarking? Why? How? (General Framework) Properties Types Limitations Attacks Current Trends

Steganography It is a sub discipline of data hiding and part of cryptology. Steganography is “secret writing”. The steganographic message is integrated invisibly and covered inside other harmless source, it is very difficult to detect the message without knowing its existence and its appropriate encoding scheme.

Digital Watermarking “Digital Watermarking “means embedding information into digital material in such a way that it is imperceptible to a human observer but easily detected by computer algorithm. A digital watermark is a transparent, invisible information pattern that is inserted into a suitable component of data source by using a specific computer algorithm. Digital watermarks are signal added to digital data that can be detected or extracted later to make an assertion about the data.

Why Digital Watermarking? In order to protect copyrighted material from illegal duplication, two typical technologies have been developed. One approach uses key-based cryptographic methods which enable the appropriate security during the transmission process, but once the encrypted data is decoded, the control of redistribution and its spread fails. To address limitations of encryption, the main idea is to label a digital material with specific marks, which are called digital watermarks. Such technology can be used as ownership proof for distribution channel tracking and other applications in business and public domains. Furthermore, watermarking technology enables the owner to obtain the copyright status of certain documents and distributors can be made accountable for the condition. Additionally, compatible media player technology (DRM used by Microsoft in Windows media player), Divx and DVD player, can detect distorted marks and refuse to play, display, or execute the media asset files

General Framework (How) In order to combine a watermark with a digital document images, you need an image (I), a signature (S=s1, s2, s3…..sN) that contains the watermarking information, and an encoding algorithm (E) to create a watermarked image (I’). The encoder takes the signature and cover the document, and generates the watermarked image, that is described as a function: E(I,S) = I’. Secret or public key and other parameters can be used to extend the watermarking encoder.

General Framework (How) The watermark is extracted using a decoder function. In this case, the decoder D loads the watermarked, normal or corrupted image I(w), and extract the hidden signature S. Using non-blind watermarking techniques, the decoder D loads an additional image I, which is often the original image, to extract the watermarking information by correlation. The process can be described as D(I,I(w)) = S. Give detail about blind and non-blind technique.

General Framework (How) Digital watermarks are weaved into the core structure of digital document in an invisible and unrecognizable way. Watermark does not change the main functionality of file. Therefore, the watermark must be inserted into the data structure imperceptibility. It should neither be visible, audible and, nor detected to strangers or observers. Each watermark method consists of an embedding algorithm and an extracting algorithm. The embedding algorithm inserts the watermark information and others only determine its existence. Such methods can be used either as ownership proof or verification.

Properties and Requirements Robustness Non-perceptibility Security Complexity Capacity

Types of Watermarking LSB Watermarking Spatial Domain Watermarking Temporal Domain Watermarking Spread Spectrum Watermarking

LSB Watermarking In general – 149 is One of the most earliest techniques Embed watermark data by alternation of certain bits of digital image which are selected based on secret key. Extraction – by reading value of bits Advantage - High Watermark channel capacity, Algorithm has less computational complexity Disadvantages-No robustness, Search Space is huge, Weak against D/A and A/D

Spatial (Space) Domain Watermarking Ueung-Mintzer scheme  Watermark is a binary logo smaller than image but stretched to form as big as image (gray scale).  Scan each pixel and extract using look up table generated using secret key.  If the extracted watermark bit is equal to the authentic watermark bit, the pixel is left unchanged; other wise the gray scale of the pixel is adjusted until the extracted watermark bit is equal to the authentic one. Wong’s public scheme  All LSB are set to zero, than image is divided into blocks, blocks applied to hash function and than applied to XOR operation. Result is encrypted using private key of RAS cryptography and embedded with original image.

Spatial (Space) Domain Watermarking continued… Wong and Memon method  Improved scheme by adding an image index and a block index to the input of hash function. Image index is just like a unique serial number of image. But the verifier needs to have the prior knowledge about the image index.

Temporal Domain Watermarking MPEG compression  I (Intra)-pictures  P (Predictive)-pictures  B (Bi-directional)-pictures I-pictures are independently encoded in MPEG, watermark insertion concentrates on I-pictures using spatial domain watermarking. It takes a watermark video that consists of a number N0 of pictures and embeds this video in the usual way, frame by frame. This number N0 is a parameter, clearly if N0=1, then we have the ordinary spatial watermarking scheme. If N0 is greater than 1, the approach is time-variant. The information contained in N0 is entirely up to the user.

Spread Spectrum Watermarking Use spread spectrum to spread the watermark all over the host image. b is the watermarking bit α is a scaling factor (Coefficient) (x,y) is a 2-dimensional pseudo-random sequence of 1 and -1 I(n1,n2) is the original image Used in radar, navigation and communication appliances

Attacks on Digital Watermarking Simple attack Detection Disabling attack Ambiguity attack Removal attack

Current Trends Color image watermarking, and other multimedia signals. Watermarking of maps, graphics and cartoons. Applications beyond copyright protection. Protocols and standardization.

References Digital Watermarking – Juergen Seitz, tech.edu/~mouli/waterm_tut.ppt+digital+watermarking+ppt&hl=en&ct=clnk&cd=2&gl=us tech.edu/~mouli/waterm_tut.ppt+digital+watermarking+ppt&hl=en&ct=clnk&cd=2&gl=us linz.ac.at/education/Inhalte/se_moderne_methoden/WS0405/hasslacher_digital_watermark ing.pdf+digital+watermarking+ppt&hl=en&ct=clnk&cd=1&gl=us linz.ac.at/education/Inhalte/se_moderne_methoden/WS0405/hasslacher_digital_watermark ing.pdf+digital+watermarking+ppt&hl=en&ct=clnk&cd=1&gl=us EU05/Notes/Watermarking.pdf+digital+watermarking+ppt&hl=en&ct=clnk&cd=3&gl=us EU05/Notes/Watermarking.pdf+digital+watermarking+ppt&hl=en&ct=clnk&cd=3&gl=us fall2001/projects/presentations/team10.ppt+digital+watermarking+ppt&hl=en&ct=clnk&cd=4 &gl=us

Any Questions….