nologies 
ography 
se a new 
'raphy is 
aves and 
rown, he 
ainst the 
n hiding 
musical 
ography. 
e art of 
whereas 
nessage. 
luding a 
>. Much 
content 
L This 
etrieving 
used by 
sages to 
tried to 
ere able 
iscovery 
U-boats. 
on about 
ipaign in 
e United 
the most 
“hese are 
ogy has 
longside 
1se extra 
etimes a 
nvisible. 
property. 
detected, 
Many 
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004 
  
photographers and studios use watermarking techniques in an 
attempt to protect their intellectual property. 
Still satellite or geo-images are all easily copied and illegally 
distributed causing the authors to lose out on considerable 
income in royalties. By embedding information in a file, 
watermarking software enables authors to control the 
distribution of and to verify ownership of their digital 
information. There are numerous steganography tools available 
on the Internet and elsewhere. The large number of 
steganography programs available also adds complexity to the 
task of recovering the hidden data from a file presumed to 
contain steganographic content. 
The rest of the paper is organized as follows: The 
Steganography and Steganographic systems are summarized in 
Section 2. The proposed method explained in detail in Section 3 
and some of the experiments are given in Section 4. The results 
and conclusions are given in Sections. 
2. STEGANOGRAPHIC METHODS 
Steganography simply takes one piece of information and hides 
it within another. Computer files such as images and audio- files 
contain unused spaces or insignificant data. Steganography 
takes advantage of these spaces by replacing them with 
information that is required to hide. The files can then be 
exchanged without anyone knowing what really lies inside of 
them. A shared image might contain vitally important 
geoinformation about the desired position over the world. 
Steganography and watermarking can also be used together to 
place a hidden trademark in images, music files, and software. 
Following features of both Steganography and Watermarking 
methods can be listed. 
A secure permutation key giving exceptional levels of 
security is used. 
- There is no need for additional metadata 
- File formats are unaltered and there is no increase to object 
data file size. 
- Digital watermarks do not affect print workflows in any 
way. 
- File transfer times remain unchanged. 
- Watermarking can support a host of standard and 
proprietary formats. 
- Embedded messages can survive high levels of data 
compression. 
Within the context of modern computing systems, 
steganography is the process of hiding secret information within 
files. Most commonly data is stored within images. Images 
make good hosts for steganographic data due to small changes 
can be made to the image without a perceivable change in the 
image characteristics. Other types of digital files also make 
good steganographic hosts such as shared movie, clip and audio 
files. Typically hidden data is stored within the least significant 
bit (LSB) of each block of data. For example, if a digital image 
were made up of a series of pixels each representing a color 
from a palette of 2" colors, each number would represent a 
shade with a value of 0 to 2"-1. Changing the shade by one 
number would not make a noticeable difference to the image. It 
is in these least significant values that steganographic data can 
be concealed. Any file format that can withstand variation 
without greatly compromising the file's integrity is a suitable 
file format for embedding information. It essentially 
“copyrights” digital information on geo-images. Steganography 
makes or read invisible signatures in the image. Certain 
steganography (Derrick 2001) techniques will also support 
change detection, data compression, integrity checking, and 
integrated metadata. Change detection lets you know when a 
feature has been modified. Data compression reduces the space 
needed to store information. Integrity checking verifies that the 
data are correctly stored and transmitted. — Metadata is 
information about the data such as how it was developed, 
processed, projected, and so on. 
3. THE DISCRETE COSINE TRANSFORM 
The discrete cosine transform (DCT) represents an image as a 
sum of sinusoids of varying magnitudes and frequencies. The 
DCT has the property that most of the visually significant 
information about the image is concentrated in just a few 
coefficients of the DCT. For this reason, the DCT is often used 
in image compression applications. For example, the DCT is at 
the heart of the international standard lossy image compression 
algorithm known as JPEG. 
The two-dimensional DCT of an M-by-N matrix A is defined as 
follows: 
  
MN z(2m-4V)p x(2n+1)g 
Brun, SN. diu Cos Cos 
m=0 n=0 
(1) 
and 
0xpzM-l 
gn @) 
sg NI 
where 
a, = 3) 
gm (4) 
  
The DCT is an invertible transform, and its inverse is given by 
MN 
  
3 (2m +p. 7(2n+1l)gq 
dun E eT B po Cos 2M Cos AN 
p=0 g=0 
(5) 
O<m=< M -1 
7 (6) 
0 <n<N-l 
2n 4l) 
au vas A AR EY ( 
pid 2M 2N 
where 
0zpzM-l 
2 (8) 
Ogi N-1