20-08-2014, 01:58 PM
Digital Tampering Detection Techniques: A Review
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INTRODUCTION
An image is a two-dimensional function, f(x,y), where x and y
are spatial (plane) coordinates and the value of f(x,y) at any
pair of coordinates (x,y) is called the intensity or gray level of
the image at that point. An image contains a lot of information
and can be monochromatic or colored. When the digital
technology is used to capture, store, modify, or view images,
they must be first converted into numbers: 1s and 0s called bits.
A combination of eight bits is called a byte. A digital image is
composed of a finite number of elements which are referred to
as pixels. A pixel is a basic unit of a colored or monochromatic
image on a computer display or in a computer generated image.
A common color image file of size 1024 X 1024 pixels and 256
colors (or 8 bits per pixel) occupies 3MB of disk or RAM
space. Since a colored image contains more information
(coloring details), so its file size is comparatively much larger
than that of monochrome. Digital images are typically stored in
either 24-bit or 8-bit files. Color variations for the pixels are
derived from three primary colors: red, green, and blue. Each
primary color is represented by 1 byte; 24-bit images use 3
bytes per pixel to represent a color value. These 3 bytes can be
represented as hexadecimal, decimal, and binary values [3].
In contrast to analog signal processing in which the image
signal is treated as a continuous signal, digital image
processing has many advantages. It allows a much wider range
of algorithms to be applied to the input data and can avoid
problems such as the build-up of noise and signal distortion
during processing. Digital image formation, the foremost step
in any digital image processing application, consists basically
of an optical system, a sensor and a digitizer. The optical signal
is usually transformed to an electrical signal by using a sensing
device (e.g. a Charge Coupled Device sensor). The analog
signal is transformed to a digital one by using a video digitizer
(frame grabber). Thus, the optical image is transformed to a
digital one. Due to inherent limitations of the processing
systems, each digital image formation subsystem may
introduce a deformation or degradation to the digital image
(e.g. geometrical distortion, noise, non-linear transformation
etc.). The mathematical modeling of the
LITERATURE REVIEW
The sophisticated and low-cost tools of the digital age enable
the creation and manipulation of digital images without leaving
any perceptible traces. As a result, the authenticity of images
can’t be taken for granted, especially when it comes to legal
photographic evidence. Manipulations on an image encompass
processing operations such as scaling, rotation, brightness
adjustment, blurring, contrast enhancement, etc. or any cascade
combinations of them. Doctoring images also involves the
pasting one part of an image onto another one, skillfully
manipulated so to avoid any suspicion. One effective tool for
providing image authenticity and source information is digital
watermarking.
CONCLUSION
Techniques and methodologies for validating the authenticity
of digital images and testing for the presence of tampering and
manipulation operations on them have recently attracted
attention. Detecting forgery in the digital images is one of the
challenges of this exciting digital age. The sophisticated and
low-cost tools of the digital age enable the creation and
manipulation of digital images without leaving any perceptible
traces. As a result, the authenticity of images can’t be taken for
granted, especially when it comes to legal photographic
evidence. Thus, the problem of establishing image authenticity
has become more complex with easy availability of digital
images and free downloadable image editing softwares leading
to diminishing trust in digital photographs. Another common
manipulation in tampering with portions of the Techniques and methodologies for validating the authenticity
of digital images and testing for the presence of tampering and
manipulation operations on them have recently attracted
attention. Detecting forgery in the digital images is one of the
challenges of this exciting digital age. The sophisticated and
low-cost tools of the digital age enable the creation and
manipulation of digital images without leaving any perceptible
traces. As a result, the authenticity of images can’t be taken for
granted, especially when it comes to legal photographic
evidence. Thus, the problem of establishing image authenticity
has become more complex with easy availability of digital
images and free downloadable image editing softwares leading
to diminishing trust in digital photographs. Another common
manipulation in tampering with portions