Computerized Image Processing for Forgery Prevention
Nathan Singleton
Computing Research
Department of Computing Sciences
Villanova University, Villanova, PA, 19085
USA
nathan.singleton@villanova.edu
ABSTRACT
The issue of copyright protection for digital media has
become a problem with rapid advancements in online
media storage. As more of these storage systems are
made, more information will be taken from them. For all
of the good that comes from new technology, an equal
amount of illegal activity can spore from it. Digital
watermarking has become one of the most popular
copyright protection methods. This paper presents
different ways in which watermarking is used, along with
the background of watermarking for personal protection
in general. There are many different aspects of digital
watermarking. This paper focuses on the main algorithms
used in the present day. It will also look into the future of
digital watermarking and how it will be able to provide
more reliable copyright protection.
KEY WORDS
Digital Watermarking, Fragile, Robust, Visibility
1. INTRODUCTION
Digital Watermarking is a process that embeds data,
called a watermark, digital signature, or tag, into a
multimedia object. The watermark can then be extorted
or detected to make a claim about the multimedia object
[1]. The multimedia object being watermarked can take
many forms, such as a digital picture, audio file, or video
clip. Watermarks have a variety of uses that include
personal protection and deterrence against theft to
maintaining data integrity, secrecy and security.
Multimedia that is stored on computers, and specifically
in the case of the example pictures included in this paper,
has always been easy to copy between computers with
minimal technical expertise. The use of computers to
transfer, post, and share work is also a relatively simple
matter by the means of websites and peer-to-peer file
sharing systems. With this straightforward and widely
available ability to share information comes an
increasingly onerous hardship for rightful owners of
digital media. Among the most common purposes of
watermarking are to maintain the rightful ownership of
digital media by the copyright holders, prevent or
discourage the pirating of digital media, and ensure that
digital media is not resold without permission of the
media owner.
2. BACKGROUND
The first use of watermarking of personal property for
purposes of security or protection is a matter of
continuing debate, although evidence indicates it may
have occurred in Bologna, Italy in 1282 [2]. This
presumed first watermark was found on an Italian piece of
paper from that time. It represented a “pomme cross with
small circles at the ends of the arms of the cross and a
large one at the centre”[2]., and although the purpose of it
is still under debate as well, there is reason to believe that
watermarks were used for similar reasons as they are used
today. Some even speculate that certain watermarks
“were used by mystical groups to carry signals with
hidden meanings,” somewhat similar to what they are
used for today [2]. Today, watermarks can be visible,
such as those embedded into images or video and
designed to be seen by the human eye, or invisible, only
detectable by computer software.
Figure 1: First know watermark [3]
3. WATERMARKING
The general form of all algorithms used to input a
watermark in an image involves the original watermark,
and the original image. The only main step found in all
watermarking techniques is the Embedding Procedure,
which places the watermark in the image. The last step is
the output, or the watermarked image. This can be seen
in figure 1.
The purpose of invisible watermarks is similar to the
purpose of visible watermarks, but with a level of secrecy
instilled. Content identification is one reason for digital
watermarking, because the rightful owner of the product
wants to have the security to know the image is his. Copy
protection is another reason for invisible watermarking
that gives the rightful owner the ability to disallow people
from using illegal copies of the image for commercial use.
Viewer tracking is a more technical use for invisible
watermarking that is especially useful for images posted
on the internet. Viewer tracking allows the owner to track
how often the image is viewed. The owner of the image,
with advanced software, can also detect if his image has
been posted illegally on other websites.
3.2 ROBUSTNESS
Figure 2: Watermarking algorithm general form [4]
3.1 VISIBILITY
Today all watermarking algorithms can be broken down
into two main catagories, visible watermarks and invisible
watermarks.
Visible watermarking techniques are
generally easily implemented and are found and can be
used in many, if not all photo editing software, such as
Adobe Photoshop or even Microsoft Paint. However if
these watermarking techniques are used the original
image might be damaged or destroyed completely.
“Visible watermarks are designed to be easily perceived
by the view, and clearly identify the owner; the
watermark must not detract from the image content itself,
however. Most research currently focuses on invisible
watermarks, which are imperceptible under normal
viewing conditions” [3]. Visible watermarks should be
used in digital libraries so that they can be used in
research papers and other scholarly works. This keeps the
image safe from commercial use.
Figure 3: Example of Visible Watermark [5]
There are two different types of robustness that are
generally taken into account when evaluating a
watermarking algorithm, Invisible –Fragile Watermarking
and Invisible – Robust Watermarking. “Invisible –Fragile
Watermarking is embedded in such a way that any
manipulation or modification of the image would alter or
destroy the watermark” [1].
In other words, the
watermark in the image would be destroyed if simple
modifications to the image are done. Fragile watermarks
are used in order to detect tampering. This is the reverse
of how one would think a watermark should work. If the
picture is tampered with the watermark will disappear and
be undetectable, and therefore the culprit will be caught.
An attacker of a fragile watermark would be successful if
he was able to alter the picture without disturbing the
watermark.
“Fragile watermarks are used for image
authentication.
Image authentication systems have
applicability in law, commerce, defense, and journalism”
[4]. A common example is the marking of images in a
memory card inside a camera. This would ensure that
photographers provide trustworthy news to consumers,
and do not broadcast false events. In most cases the
watermark placed into a fragile watered image cannot be
taken out. For example when this implementation is used
in a digital camera, the watermark is placed directly after
the image is taken, and the owner does not know the
difference.
Host Pixel: 10110001
Secret Pixel: 00111111
New Image Pixel: 10110011
Figure 5: Least Significant Bit Algorithm example [8]
Figure 4: General Algorithm for Fragile Watermark Detection
[6]
Robust Watermarking has proven to be a more prevalent
research topic in the area of Digital Watermarking.
“Robust watermarks withstand moderate to severe signal
processing attacks (compression, rescaling, etc.) on an
image” [4]. In other words, they have the ability to be
compress, such as with jpeg compression, and keep the
information stored inside. Robust Watermarks also keep
their information hidden when cropped or rotated as well,
unlike with all fragile watermarks. A robust watermark is
implemented by embedding a host signal in an image so
that the removal of the said signal is complex without
corrupting the original image [5]. This type of invisible
watermarking has many real world applications. It is
used, for example, when the seller of digital images in
concerned that his fee-generating images may be obtained
by a person who will make them available for free [1].
This would make it so that the owner is not paid for the
work put into the product.
This is seen as a fragile technique, because if the new
image is tampered with it is easy for computer software to
detect. This is because the software that would detect
these interferences only has to compare it with an
originally made image.
A different watermarking algorithm involves Discrete
Cosine Transform or DCT. The watermark is added to
the image by manipulating the frequency coefficients in
the DCT. With complicated algorithms, the area of the
picture with the least “noise,” or amount of different
shades of color, is chosen to hide the information relating
to the watermark. This form of watermarking changes the
brightness of the image slightly, and is not visible to the
human eye, only the software used to create the
watermark.
4. DIGITAL WATERMARKING
METHODS
There are a variety of techniques to watermark a digital
image. The following are descriptions of two of the less
complex and more easily understood models. The first
algorithm is called least significant bit manipulation. This
may seem like a simple algorithm, but it has been proven
to be effective at hiding the watermark successfully. The
first step in this is to choose how many bits you want to
hide the secret image in [6]. This beginning step can
make or break how well the algorithm works, the more
bits used to hide the secret image, the more the image
original image will break down. However, the more bits
used to hide the secret image the more likely you will get
all of the information out. After you have chosen the
number of bits to represent the secret image, you must
create a new image by combining the most significant bits
of each picture. The most significant bits of the original
will stay as the most significant bits in the combined
version. The most significant bits of the secret image will
become the least significant bits in the combined version.
Not Watermarked
Figure 6: DCT algorithm used
Watermarked
When research was started on digital watermarking , it
was found that it is a very broad field. A large majority
of the information that was found were research papers
that were abstract and helped find specific areas of
interest that helped write the paper. First of all, it was
necessary to delve into the background of watermarking
in general to see how it was used in the past, and how it
continues to be used today. After more research,
visibility aspects of digital watermarking and what the
stipulations are that make powerful watermarking
algorithms needed to be discovered. Visibility leads to
robustness and a great deal more understanding of the
subject as a whole. After finding more information on
how a watermarking algorithm is made and used, research
papers were analyzed in depth and with more force.
However, they proved to be very technical, with few or no
examples. Digital watermarking will only grow as
companies keep finding new and better ways to protect
information.
.
5. PROPOSED WORK
Research has found many watermarking algorithms that
are visible, invisible, robust, and fragile. However there
is always room for improvement. Future work in the
field of digital watermarking should try to encompass
multiple layers of watermarks. This is because a visible
watermark is unreliable and is not able to fully protect
against attacks from users on the internet. The problem
with an invisible watermark is that the person viewing the
webpage where media is displayed may or may not know
if it is copyright protected or not. It is up to the owner of
the web page to provide valid documentation that states
the image is under copyright protection. Therefore
having two layers of watermark, visible and invisible, will
allow for a direct knowledge to the user visiting the
website that the image is under copyright, and should not
be tampered with.
A way in which this could be done is with some
watermarking algorithms that are already in existence.
More research will be needed to determine which aspects
of certain watermarking techniques will be retained, but
after a short time coding will be able to be undertaken.
Some specific watermarking techniques that have been
simple to understand may be a stepping stone in working
towards an interface that will accomplish the goal of
applying both a visible and invisible watermark on a
digital image. One major problem that may hinder
progress on this project is what mark to put on the image
first. If a plan is devised to put an invisible fragile
watermark on the image, the visible watermark must be
put in place first. This is because any alteration to the
digital image after the invisible watermark is put in place
destroys it.
As a first scheme for a method to implement the said
proposal, a visible watermark would be placed on the
image. This would be done with a program like gimp or
photoshop that has the ability to filter opacity levels in
order to not disrupt the image much as a whole. Some
testing has already been done in this area as seen in figure
6. In order to decrease time spent on formatting in
photoshop a user interface that loops through pictures
would be more suitable.
Figure 6 Personal Library
After a plan is found that cycles through photos in order
to put a visible watermark on the image, the invisible
watermark needs to be put in place. In realistic terms the
watermark would be a fragile watermark, due to its fast
execution time. As found in previous research a hash
function will have to be devised that manipulates the LSB
of each pixel in the image [9]. The general form of the
function to do this might look similar to other research in
the fragile watermarking field.
L(i,j) = fR(R(i,j))fG(G(i,j))fB(B(i,j))
for each pixel (i,j)
f:COLOUR(i,j): {7 MSBs}  {0,1}
(hash function with a key)
f:fcolour(binary) : LSB substituted colour
value
Colour = {R, G, B}
i,j : integer variables.
Figure 7: Fragile Watermarking Algorithm [9]
By implementing the watermark in Figure 7 on a digital
image that a visible watermark has been placed on, more
security is placed on the image.
5.1 QUALIFICATIONS
This project would be able to be done due to experience
using programming languages such as python. During
time spent being a teacher’s assistant in the class
Computing with Images I have become accustomed with
programming concepts involved in pixel manipulation.
Further experimentation would be needed in order to
handle the project at hand, but with my experience
teaching the subject, I believe I have a firm grasp on the
task at hand. Along with programming experience from
classes such as Analysis of Algorithms and Computer
Systems the proposed work would be able to be
accomplished.
5.2 TIMELINE
During the first two weeks of the project further research
for invisible watermarking algorithms that may be
implementable would be done. This may add work onto
the end of the project, but more understanding of past
problems and solutions is needed before coding is actually
done. The next stage in the proposed work would be to
devise and implement an algorithm that cycles through
digital images in order to place on a visible watermark.
The implementation of this algorithm would be the next
two weeks of the timeline. After the first month is
complete, hopefully all research for the invisible
watermark and coding for the visible watermark will be
complete. Once this is done the next two weeks will be
allocated to implementing the invisible watermarking
algorithm that has been found to be the most suited for the
project at hand. If all goes according to the plan stated
above, the project will be complete in six weeks.
6. CONCLUSION
When research was started on digital watermarking , it
was found that it is a very broad field. A large majority
of the information that was found were research papers
that were abstract and helped find specific areas of
interest that helped write the paper. First of all, it was
necessary to delve into the background of watermarking
in general to see how it was used in the past, and how it
continues to be used today. After more research,
visibility aspects of digital watermarking and what the
stipulations are that make powerful watermarking
algorithms needed to be discovered. Visibility leads to
robustness and a great deal more understanding of the
subject as a whole. After finding more information on
how a watermarking algorithm is made and used, research
papers were analyzed in depth and with more force.
However, they proved to be very technical, with few or no
examples. Digital watermarking will only grow as
companies keep finding new and better ways to protect
information.
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