Abdelkader H. Ouda, Fall 2004,
"Digital Watermarking Techniques for Image Security
and Hidden Communication",
Computer Science Department,
University of Western Ontario, Canada.
Ph.D. Thesis Abstract
Popular media (television, movies, magazines, etc.) has
frequently tried to present information in the form of images.
The question is then raised, "Are we going to authenticate the
images that we have just seen?". The answer could come down to
the level of trust in the photographer and media outlet.
However, in our present globalization era, this generally is
not achievable. Thus, unless we have image authentication
techniques, such images will be difficult to verify.
Suppose that you have posted a rare (valuable and/or unique)
photograph on your website. If this photo appears in another
medium, such as a famous magazine, where the credit and money
go to someone else, are you able to prove your ownership for
this photo? Unless you have used image copyright protection
techniques to encode your copyright information on your
digital photograph before putting it on your website, you
In addition, one can encode secret information in the image
allowing the secret information to be sent in an environment
where encryption is not permitted. This might be done using
"Hidden Communications" techniques. These techniques could
allow the exchange of secret messages without attracting much
attention. The main contribution of this dissertation is the
development of three promising digital watermarking
techniques, which enable image authentication, copyright
protection, and hidden Communication.These techniques are
designed using two kinds of technologies, namely cryptography
and steganography. Cryptography can be defined as a science
of secret writing, whereas steganography is the art and
science of communicating in a way, which hides the existence
of the communication.
An image dependent hashing function is proposed, which
utilizes correlation coefficients statistics to measure the
image pixels relationships. This function produces an image
dependent hash value that is quite short when compared with
those produced by other cryptographic hashing functions.
Also, a new watermark embedding approach is introduced, where
the cryptosystem is used to embed the watermark rather than
encrypt the watermark itself. This approach helps increases
the localization accuracy for most existing block-based
watermarking techniques. Hence, a novel image watermarking
technique for image authentication has been implemented. This
technique is able to provide greater assurance that the image
has not been modified. However, if modifications occur, the
location of these modifications will be accurately identified.
An enhancement to the general steganography model has been
made. This enhancement adopts a cryptographic shared key
mechanism, where a new key generation module is introduced.
It generates a shared secret key between parties based on
their public information. This enhancement affects the vast
majority of watermarking techniques, either for copyright
protection or hidden communication.
Moreover, a new approach for information hiding is
introduced. This approach is compatible with the JPEG2000
image compression standard. The information will be embedded
during the rate/distortion optimization phase. While the
capacity of the hidden information is inversely proportional
to compression level, the hidden information is robust
against the JPEG2000 compression ratios. Finally, an image
copyright protection technique that utilizes this approach
Keywords: digital watermarking, steganography, cryptography,
information hiding, image authentication, copyright
protection, and hidden communication.