1. Steganography in digital images
Tapadhir Das
CS 674

2. Contents What is Steganography? Usages Steganographic Methods Spatial
Frequency
Steganalysis

3. Steganography
Science involving secretive communication through multimedia: images, videos, or audio
This presentation focussed on digital images.
Cover image: Main image on which messages or files get encoded.
Stego image: Cover image after embedding and encoding.

4. ‘‘Compliments of CPSA MA to our chief Col Harold R
‘‘Compliments of CPSA MA to our chief Col Harold R.Shaw on his visit to San Antonio May 11th 1945’’

6. Usages Secretive communication
Copyright control of materials (watermarking)
Safe circulation of sensitive data for organizations
Image enhancement

7. Steganographic Methods
Basic Idea:
Types of Steganography:
-Spatial
-Frequency
-Adaptive

8. Spatial Method Steganography in the spatial domain of images.
Pixel value manipulation.
LSB manipulation

10. A B C
D E F

11. JPEG Compression 2D DCT = Discrete Cosine Transformation
Where M and N are the dimensions of the cover image.
Each image is broken down to multiple cosine waves with coefficients
Low frequencies usually have higher coefficients and vice versa

12. Frequency Method
LSB manipulation performed on high coefficient frequencies in every 8x8 block.
Example::
Coefficient is 202 =
201 =
Common Algorithms: JSteg, OutGuess, F5

13. Steganalysis Defined as science of attacking steganography. Method:
Visual Attack
Image Filtering, Rotation, Cropping
Histogram Analysis
Other Methods: X2-Test, Stegdetect, Fridrich’s Algorithm, RS- Steganalysis, Machine Learning using a Deep Neural Network.

14. References https://en.wikipedia.org/wiki/Steganography