Cryptography Reference
In-Depth Information
to achieve the objective of notifying and protecting the copyright of digital images
simultaneously, the following is used. The DCT coe
cients of each image block are
divided into two parts for embedding the visible and invisible watermarks, respec-
tively. The visible watermark is embedded in the DC DCT coe
cient and most of the
AC DCT coe
cients of each block, and the invisible watermark in the rest. Based
on the characteristics of the Human Visual System (HVS), the embedding strength
of the visible watermark is varied in accordance with the underlying content of the
host image. The invisible watermark is embedded in a selection of midrange frequen-
cies. Experimental results show that the visible watermark is hard to remove and
the invisible watermark is robust to common digital signal processing operations.
For the third application, we deal with an image database as follows. First, several
important features are computed o
ine for each image in the database. Then, the
copyright, annotation and feature watermarks are embedded o
ine into all images
in the database. During the online retrieval, the query image features are compared
with the extracted features from each image in the database to find the similar
images. Experimental results based on a database with a 1000 images in 10 classes
demonstrate the effectiveness of the proposed scheme.
11.1 Introduction
Digital multimedia is today largely distributed over the Internet and via CD-
ROM. The possibility of lossless and unlimited copies of digital contents is
a major obstacle from the owners viewpoint when considering entering the
digital world. The amount of audiovisual information available in digital for-
mat has grown exponentially in recent years, and has resulted in informa-
tion an explosion which has exceeded the limit of acceptability. Digitization,
compression, and archival of multimedia information has become popular,
inexpensive and straightforward. Subsequent retrieval of the stored informa-
tion might require considerable, additional work in order to be effective and
e
cient. Copyright notification, copyright protection, copy protection, con-
tent authentication and multimedia retrieval have therefore become the five
important issues in the digital world. This chapter considers following three
applications for images: (1) to achieve the goal of content authentication and
copyright protection simultaneously; (2) to notify and protect the copyright
of digital images simultaneously; (3) provide a multipurpose watermarking
scheme for image retrieval.
Conventional cryptographic systems permit only valid keyholders access
to encrypted data. Once such data is decrypted there is no way to track its re-
production or retransmission. Over the last decade, digital watermarking has
been presented to complement cryptographic processes. In general, there are
two types of digital watermarks addressed in the existing literature, and they
are visible and invisible watermarks. The invisibly watermarked digital con-
tent appears visually to be very similar to the original. Invisible watermarks
can be broadly classified into two types, robust and fragile or semi-fragile wa-
termarks. Robust watermarks [1, 2, 3, 4, 5, 6] are generally used for copyright
