HIDDEN COMMUNICATION IN FREQUENCY DOMAIN FOR INFORMATION 
EXCHANGE 
F. Gónül Toz* H.M. Palanctoëlu°, E. Besdok b 
? [TU, Civil Engineering Faculty, 80626 Maslak Istanbul, Turkey - tozg@itu.edu.tr 
° Erciyes University, Engineering Faculty, Geodesy and Photogrammetry Dept., Kayseri, Turkey, (hpalanci 
,cbesdok)@erciyes.edu.tr 
Commission VI, WG VI/4 
KEY WORDS: Spatial Information Sciences, Technology, Application, Data Mining, Pixel, and Theory... 
ABSTRACT: 
In last decade, Geoinformatic products such as geo-maps and aerial photos have been shared over the Web. The Web technologies 
have been employed in providing geo-information exchange. Today, there is a need to employ efficient tools such as Steganography 
to save copyrights of producers and prevent the unauthorized users from non-public geoinformation. In this paper, we propose a new 
method of hiding colored geo-images within gray scale images using Steganography methods. 
1. INTRODUCTION 
Cartography is the science of making maps. Though hand- 
drawn cartography is still prevalent, traditional drafting is being 
rapidly replaced by computers and graphics software, which 
allow maps to be created quickly and accurately. Complex geo- 
maps are made with sophisticated scanning equipment, while 
simpler geo-maps can be drawn on a personal computer. 
Generally, cartographers begin with a grid such as the latitude 
and longitude to which they add such information as streets, 
population density, and physical features. Many cartographers 
are employed by the governments around the world to make 
geo-maps for various purposes. Some of the geo-maps have 
been prepared for only authorized users. The Army Forces also 
employ cartographers for private purposed geo-map making. 
There are many companies making and selling all kinds of geo- 
maps from subsurface geo-maps to geo-thematic maps. In some 
countries, some kind of geo-maps such as militarial geo-maps 
or subsurface mine geo-maps have been prohibited to produce 
and use by unauthorized users. All public and private 
organizations have to secure their geoinformation based 
products in order to control their commercial market or rights. 
However, when they have to share some geoinformations over 
communication cannels such as over Web, some undesired and 
unsafe conditions could appear. The shared geoinformation 
should be hidden within a desired container signal such as 
images or audios in order to provide secure communication 
process. 
C^ ganography (Derrick 2001, Gruhl 1998, Anderson 1996, 
Anderson 1998, Arnol’d 1992, Cachin 1998, Chang 1997, 
Csiszar 1978, Currie 1996, Tsai 2002, Dijk 1997, Ettinger 1998, 
Kahl 1996, Kurak 1992, Menezes 1997, Mittelholzer 2000, 
Ptzmann 1996) is the art of hiding the existence of a message. 
The word Steganography comes from the Greek words steganos 
(secref) and graphy (writing). An example could be a letter 
written with two different inks. When the letter is submerged in 
water one of the inks dissolves while the other remains on the 
letter, thus revealing the secret message. The original message 
on the letter is just a cover to hide the existence of the secret 
message. Steganography is hiding the very existence of 
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communication. One famous example of early steganography is 
that of Herodotus who shaved the head of one of his slaves and 
tattooed a message on his head. After his hair had re-grown, he 
was sent to deliver a message to instigate a revolt against the 
Persians. Steganography has a wide range of forms from hiding 
messages in the soles of shoes to hiding messages in musical 
scores. 
Steganography is sometimes confused with cryptography. 
Cryptography (Menezez 1997, Schneier 1994) is the art of 
concealing the contents of a message (encryption) whereas 
Steganography is the art of hiding the existence of a message. 
The message can be any type of digital information including a 
simple text file, a JPEG image, or any other type of file. Much 
of the available software that embeds steganographic content 
into a host file often employs cryptography as well. This 
greatly adds to the complexity and difficulty of retrieving 
concealed content. 
One of the earliest examples of cryptography was used by 
Julius Caesar (Kahl 1996) when he sent military messages to 
his armies. Perhaps since that time, people have also tried to 
decode encrypted messages. Allies in World War II were able 
to break a secret German code called Enigma. This discovery 
enabled Allied forces to locate and sink many German U-boats. 
Moreover, they were able to obtain advanced information about 
German military operations that was critical to the campaign in 
Europe. Similar code-breaking abilities also allowed the United 
States Navy to intercept the Japanese fleet in one of the most 
decisive battles in the Pacific--The Battle of Midway. These are 
just a few examples of how cryptographic technology has 
played an important role in history (Kahl 1996). 
Watermarking (Derrick 2001) is often discussed alongside 
Steganography. It is similar to Steganography because extra 
information is kept embedded in the image. Sometimes a 
watermark is visible and sometimes it is invisible. 
Watermarking is widely used to protect intellectual property. 
Whereas Steganography seeks to go unseen and undetected, 
watermarks seck to be robust (difficult to remove). Many 
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