multimedia copyright protection technologies m. a. suhail, i. a. niazy [email protected]
TRANSCRIPT
Introduction
There are various watermarking schemes applied to images.
The purpose is to give an overview about the field of invisible watermarking.
I will discuss the basic concept, procedure, applications, and requirements needed.
Digital Watermarking Concept
An identification code carrying information about the copyright owner, the creator of the work, etc., embedded permanently into digital data.
The purpose of embedding WM is to protect copyright or checking for modifications.
Types of Watermarks
There are two major categories for digital watermarking:– Visible Watermarking
• Like stamping on paper
– Invisible Watermarking• Far more complex• I will focus on this category
Invisible Watermarking
Used to identify copyright data The most suitable media for Watermarking
are still images, video, and audio. Unsuitable media include:
– Executable files• Converting it to conical format
– Text• Can be overcome by any commercial OCR.
How to Embed a Watermark
Encoder (E)
Key (PN)
Original MediaSignal
(I0)
Watermarked Media signal
(I water)
Watermark W
How to Embed a Watermark (continued) The previous figure may be expressed
as follows:– E(I0, W) = Iwater
– Embedding function ‘E’ modifies I0 according to W.
How to Detect a Watermark
Pirate product Attacked Content Decoder
Decryption Key
Decoder response:Is the watermark W present? (Yes/No) Z
How to Detect a Watermark (continued) Detection Function (Decoder) ‘D’ is
defined as: D(R, I0) = W’, where R is the watermarked signal.
W’ is compared with W, based on a correlation measure:
where c is the value of the correlation, and 0 is a threshold.
otherwise
cWWZ
0
1),'( 0
Robust Watermarking Scheme Requirements Imperceptibility (Perceptual Invisibility)
– Penalty: less robustness Robustness
– Should survive intentional or unintentional attacks.– With images, resistance with geometric
manipulation is still an open issue Detectability
– Small probability of failing
Digital Watermarking Techniques
D ig ita l W ate rm ark in g Tech n iq u es
V is ib le W ate rm ark in g
W ave le t Tran s fo rm D isc re te C os in eTran s fo rm (D C T)
F rac ta l Tran s fo rm
Tran s fo rm D om ain
L eas t S ig n fican t B itM od ifica tion (L S B )
S p atia l D om a in
In vis ib le W ate rm ark in g
D ig ita l W ate rm ark in g
Digital Watermarking Techniques (continued) Spatial Domain Techniques
– The modification of LSB (Least Significant Bit) of the host data techniques are used in the spatial domain.
– LSB is modified using fixed magnitude NP sequence.
– The LSB is insignificant, so the WM will be invisible.
– WM easily corrupted by signal processing.
Digital Watermarking Techniques (continued) Transform Domain Techniques
– DCT (Discrete Cosine Transform) is based on dividing the image to square blocks of size 88, then modifying middle range frequency DCT coefficients of selected blocks.
– Wavelet Transform: Multi-resolution based technique.
– Fractal Transform: Very few works, because computationally expensive.
DCT Transform WatermarkOrginal Image Watermarked Image
Absolute difference
0 200 400 6000
0.05
0.1
0.15
0.2
0.25
Watermarks
DetectorRespose
Magnitude of the detectorresponse
OutputThreshold
A mosque and its watermarked image with the detector response.
Commercial Software for Watermarking Direct-Sequence
– Adds noise to every element in the document. and Frequency-Hopping
– Selects a pseudorandom subset of data to be watermarked.
Direct-Sequence and Frequency-Hopping spread-spectrum are the methods used for most commercial watermarking.
Common Commercial Software
Digimarc® Uses Direct-Sequence methods to superimpose a watermark over an image.
SysCoP® is also another common software.
Commercial software lack some means of security in order to keep their prices within a reasonable bound.
Digimarc® Software Example
a b
(a) A watermarked image using Digimarc® software, and (b) the watermark information of (a) by Digimarc® displayed in a window. The bar in the bottom of the window displays the robustness of the watermark.
Conclusion
The concept and types of digital watermarking is defined.
Next, The usage and suitable media for invisible Watermarking is discussed.
Also the Digital Watermarking techniques were described.
Finally, some Commercial Software and their drawbacks were described.
