image steganography

1. IMAGE
STEGANOGRAPHY
Guided By:
Prof. Nikunj Gamit
Prepared By:
Nidhi Papaiyawala
201203100810041
(6th IT)

2. Content
 Definition of image steganography
 Advantages
 Limitations
 Application
 Block diagram of steganography
 Different techniques
 Introduction of LSB technique
 Merits and Demerits of LSB
 Introduction of DCT technique
 Application
 Error analysis
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3. Image steganography
 Definition:
Steganography is the art of “concealed
writing” and it refers to techniques that hide
information inside objects known as “Cover
Objects”.
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4. Advantages of steganography
 The secret message does not attract attention to
itself as an object of scrutiny.
 steganography is concerned with concealing a
secret message is being sent, as well as
concealing the contents of the message.
 Difficult to detect. Only receiver can detect.
 Provides better security for data sharing.
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5. Limitations
 The confidentiality of information is maintained
by the algorithms, and if algorithms are known
then this technique is of no use.
 Password leakage may occur and it leads to the
unauthorized access of data.
4

6. Application
 several information sources like our private
banking information, some military secrets, can
be stored in a cover source.
 Steganography is used by some modern printers
and color laser printers.
 Steganography can be used for digital
watermarking.
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7. Basic Block diagram
Embedding information:
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Embedding
Process
Stego-Key
Embedded
message
Cover
Image
Stego
Image

8. (cont.)
Extracting information:
7
Extracting
Process
Stego-Key
Cover
Image
Stego
Image
Embedded
message

9. Different Techniques[1]
There are two categories:
1)Spatial Domain:
which mainly includes LSB(Least
Significant Bit)
2)Frequency Domain:
which includes DCT(Discrete cosine
transform) and Wavelet Transform.
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10. Least Significant Bit
 Simple approach to embedding information in
a cover image.
 It operates on principle that the human eye can
not differentiate between two shade separated by
only one bit.
Algorithm to embed the message:[1]
 Read the cover image and text message which is
to be hidden in the cover image.
 Convert the color image into grey image.
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11. (cont.)
 Convert text message in binary.
 Calculate the LSB of each pixel of cover image.
 Replace LSB of cover image with each bit of
secret message one by one.
 Write stego image.
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12. Algorithm to extracting message
 Read the stego image.
 Calculate the LSB of each pixel of stego image.
 Extract the bits and covert each 8 bit in to
character.
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13. Result of LSB
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Cover image Stego image

14.  Merits
1) Simple to
implement.
2) High payload
capacity.
3) Low complexity.
 Demerits:
1) Vulnerable
corruption.
2) Vulnerable to
detection.
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15. DCT(Discrete cosine transform)
 The DCT transforms a signal or image from the
spatial domain to the frequency domain.
 Grouping the pixels into 8 × 8 pixel blocks and
transforming the pixel blocks into 64 DCT.
 DCT allows an image to be broken up into
different frequency bands namely the high,
middle and low frequency bands
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16. Process of DCT based image
Steganography are as follow:[2]
Embedding information:
 Load cover image and secret image.
 Divide the cover image in to 8x8 blocks of
pixels.
 Transform the cover image from spatial domain
to frequency using two dimensional DCT .
 Quantize the DCT coefficients by dividing using
factor in to the rounded value. 15

17. (cont.)
 Encrypt the secret image using RSA algorithm.
 Divide the encrypted image in to 8x8 blocks.
 Embed this data in the mid DCT coefficients of
cover image.
 Apply two dimensional inverse DCT to view it
in the spatial domain.
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18. Block Diagram of DCT[2]
secret
message
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Encryptio
n
Embeddi
ng
2D DCT
on each
block
8*8 block
preparatio
n
Cover
image
2D IDCT
on each
block
Stego
Embedding information:

19. Extracting information
 Read the Stego image.
 Divide the stego image in to 8x8 blocks of
pixels.
 Transform the stego image from spatial to
frequency domain by applying two dimensional
DCT on each block
 Quantize the DCT coefficients in to the rounded
value.
18

20. (cont.)
 Extract the encrypted image values from mid-
frequency coefficients.
 Decrypt the values using RSA algorithm.
 Apply two dimensional inverse DCT to view the
extracted image in the spatial domain.
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21. Extracting information[2]
20
Stego
image
8*8 block
preparatio
n
2D DCT
on each
block
Extraction
2D IDCT
on each
block
Decryptio
n
Extracted
image

22. Result of DCT
21
Cover Image Secrete Image

23. Output at the receiver side
Cover Image Stego Image
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24. Advantages
 Energy compaction.
 High compression ratio,
 Small bit error rate
 Good information integration ability.
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25. Application
 It is often used in image processing, especially
for lossy compression, because it has a strong
"energy compaction" property.
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26. Error Analysis [2]
(I)Bit Error Rate(BER):
 For the successful recovery of the hidden
information the communication channel must be
ideal.
 for the real communication channel, there will
be error while retrieving hidden information and
this is measured by BER.
all pixel
BER= 1 ∑ |image cov -image steg |
|image cov| i=0
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27. (cont.)
(II)Mean Square Error:
 It is defined as the square of error between cover
image and stego image.
 The distortion in the image can be measured
using MSE and is calculated using Equation
n
MSE = 1 ∑ (cov-steg)2
n i=0
26

28. (cont.)
(III)Peak Signal to Noise Ratio (PSNR)
 It is the measure of quality of the image by
comparing the cover image with the stego
image, i.e. Difference between the cover and
Stego image is calculated using Equation.
PSNR = 10log10 2552/MSE
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29. Conclusion.
 Steganography is the art and science of writing
hidden message that no one apart from the
sender and receiver, suspect the existence of the
message.
 DCT-Steganography is based on encryption. To
provide high security Steganography and
cryptography are combined together. This
technique encrypts secret information before
embedding it in the image.
 Larger PSNR indicates the higher the image
quality . a smaller PSNR means there is huge
distortion between the cover-image and the
stego image.
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30. References
 Anil k Jain, “Fundamentals of digital image
processing", University of california-
davis,prentice hall.
 Proceeding of the 2006 International conference
on “Intelligent information hiding and
multimedia signal processing 2006 IEEE.
 K.B.Raja', C.R.Chowdary2, Venugopal K R3,
L.M.Patnaik , A Secure Image Steganography
using LSB, DCT and Compression Techniques
on Raw Images,2005 IEEE 29

31. THANK YOU
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