Visual Data hiding technique described as Steganography.

1. Steganography
NAME --Santu Chall
Roll No – 001130401005
Dept. – School of Education Technology
Course – Master in Multimedia Development

2. What is Steganography ?
• Comes from greek
‘steganos’ – covered
‘graphie’ – writing
• Steganography is the art and science of
writing hidden messages in such a way
that no one apart from the intended
recipient knows of the existence of the
message.
• Carrier: text, image, video, audio, etc.
Stegosaurus: a covered lizard
(but not a type of cryptography)

3. What is Computer Image
• Computer image is an array of pixels
• Pixels represent different light intensities
Are encoded as bit patterns
• Bit-depth
8bit grayscale – 256 levels of gray
24bit RGB – 16,777,216 million colors

4. Image Compression
• Lossy vs Lossless Compression
• Lossy (JPEG)
Discards excess image data, removes details that are too
small for human eye to differentiate.
Smaller file size.
• Lossless (TIF,BMP,GIF)
No loss of data, uncompressed image bit-by-bit identical
to original.
Larger file size.

5. Steganography Techniques
• Least-significant bit modifications(LSB)
• Masking and filtering
• Transformations

6. Least-significant bit
modifications(LSB)
• Most popular technique when dealing with
images
• Replaces least significant bits with the message
to be encoded
• Simple, but susceptible to lossy compression
and image manipulation

7. Uses of LSB
• Storing passwords and/or other confidential
information
• Covert communication of sensitive data
• Speculated uses in terrorist activities
• Being widely used to hide and/or transfer
illegal content

8. MASKING & FILTERING
• Masks secret data over the original
data by changing the luminance of
particular areas
• During masking, it embed the
message within significant bits of the
cover image
• Not susceptible to lossy techniques
because image manipulation does not
affect the secret message

9. Uses of MASKING & FILTERING
• Digital Watermarking – provides
identification pertaining to the owner;
i.e. license or copyright information
- Invisible vs Visible
• Fingerprinting – provides
identification of the user; used to
identify and track illegal use of
content

10. TRANSFORMATION
• Discrete cosine transformations
(DCT)
• Hiding in Frequency Domain

11. Uses of TRANSFORMATION
• Harder to implement
• More Robust against attack and
alteration
• Can be used in lossy compression
• Very Hard to detect as changes in
frequency domain are orders of
magnitude smaller than signal

12. Basics of Modern Steganography
fE: steganographic function "embedding"
fE-1: steganographic function "extracting"
cover: cover data in which emb will be hidden
emb: message to be hidden
key: parameter of fE
stego: cover data with the hidden message

13. DETECTING STEGANOGRAPHY ON
IMAGE
• Most Steganography algorithm are used LSB.
• Uses the Stastical Analysis on the LSB.
• Detect the secret data using the DCT method
while using the loosy format picture.

14. DRAWBACKS and RECOVER FROM
STEGANOGRAPHY IN IMAGE
• Do not uses loosy compression technique .
• Do not resize images.
• Do not convert to an image to another
format image.
• Do not change the luminance of an image.

15. SUMMARY
• Steganography as a whole has existed in many
forms throughout much of history.
• Lossless compression of images with a great
deal of color variation work best as a cover
image to embed a message.
• Steganography can be used as beneficial tool
for privacy

16. 1.http://en.wikipedia.org/wiki/Steganography
2.http://www.jjtc.com/stegdoc/index.html
3. C. Kurak, J. McHugh, "A Cautionary Note On
Image Downgrading," IEEE Eighth Annual Computer Security
Applications Conference, 1992.