IMAGE REPLICA DETECTION USING R-TREES AND LINEAR DISCRIMINANT ANALYSIS
Spyros Nikolopoulos, Stefanos Zafeiriou, Panagiotis Sidiropoulos, Nikos Nikolaidis and Ioannis Pitas
Dept. of Informatics, Aristotle University of Thessaloniki, Box 451, 54124 Thessaloniki, Greece
e-mail: {nikolaid,pitas}@aiia.csd.auth.gr
ABSTRACT
In this paper a novel system for image replica detection is
presented. The system uses color-based descriptors in order
to extract robust features for image representation. These fea-
tures are used for indexing the images in a database using an
R-Tree. When a query about whether a test image is a replica
of an image in the database is submitted, the R-Tree is tra-
versed and a set of candidate images is retrieved. Then, in
order to obtain a single result and at the same time reduce
the number of decision errors the system is enhanced with
Linear Discriminant Analysis (LDA). The conducted experi-
ments show that the proposed approach is very promising.
1. INTRODUCTION
Recent technological advances in the area of multimedia con-
tent distribution have resulted in a major reorganization of
this trade. Valuable digital artworks can be reproduced and
distributed arbitrarily without any control by the copyright
holders. Thus, issues related to intellectual property rights
protection arise.
Numerous systems addressing the issue of copyright pro-
tection can be found in the literature, the vast majority of them
being based on watermarking. Watermarking is the technique
of imperceptibly embedding information within the content of
the original image [1]. Although watermarking has attracted
considerable interest from both industry and academia, it bears
certain deficiencies. The requirement of embedding informa-
tion inside a digital image before it is made publicly avail-
able, automatically excludes digital images that are already
in the public domain and need to be copyright protected. In
addition, watermarking is unable to counter content leakages,
when an unwatermarked copy of the original artwork is stolen.
In order to overcome these inherent watermarking defi-
ciencies, the scientific community recently started to investi-
gate image copyright protection and Digital rights Manage-
ment from another perspective. Specifically, the problem is
envisaged as an image similarity one where the system de-
cides if a query image resembles a reference image (i.e. it is a
This work has been partly supported by EU and Greek national funds
under Operational Programme in Education and Initial Vocational Training
II through the Archimedes project ”Retrieval and Intellectual Property rights
protection of Multidimensional Digital Signals” (04-3-001/4).
replica of this image). These systems are referred to as image
replica recognition/detection systems [2, 3, 4, 5]. Replica de-
tection is the process of identifying all images that have been
generated from the original version through intentional or un-
intentional manipulations. It is assumed that the modified im-
ages maintain sufficient visual quality in order to keep their
commercial value and also maintain the semantic content of
the original. Severely distorted copies are of no interest for a
replica detection system. The major benefit of this approach
derives from the fact that no additional information should be
embedded within the image content, thus making the system
applicable to images that are already in the public domain.
In this paper an image replica detection system that uti-
lizes a database of original images that can be queried with a
suspect image and decide whether this image is a replica of a
stored original is proposed. Images are represented by a fea-
ture vector comprising of color-based descriptors [6]. Then,
we implement a multidimensional indexing structure based
on R-Trees. Although substantially reduced, the probability
that the R-Tree returns more than a single image as candidates
for being the originals of the query is existing and prevents
the system to decide unambiguously. We introduce the use
of image-class information for resolving cases unsuccessfully
handled by the indexing structure. Specifically, LDA (pre-
ceded by PCA) is applied in order to reformulate the solution
space and yield more discriminant image representations.
2. REPLICA DETECTION SYSTEM
2.1. System Overview
The process of engineering the proposed image replica detec-
tion system can be separated to two independent phases. The
first phase deals with the database organization and construc-
tion. Each time a new original copyright protected image is
added into the database, the image is subjected to a series of
predefined attacks (image manipulations) selected according
to the system’s design specifications. Feature vectors are ex-
tracted from each attacked version resulting in a feature table
which contains samples from the feature space neighborhood
of the original image. The latter is utilized for the calculation
of an extent vector that specifies the neighborhood extent for
each dimension. Finally, the original image is indexed within
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