Image steganography

IMAGESTEGANOGRAPHY

Guided By:Prof. Nikunj GamitPrepared By:Nidhi Papaiyawala201203100810041 (6th IT)

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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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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Advantages of steganographyThe 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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LimitationsThe 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.

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Applicationseveral 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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Basic Block diagramEmbedding information:

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EmbeddingProcess

Stego-Key

Embeddedmessage

CoverImage

StegoImage

(cont.)Extracting information:

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ExtractingProcess

Stego-Key

CoverImage

StegoImage

Embeddedmessage

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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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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(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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Algorithm to extracting messageRead 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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Result of LSB

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Cover image Stego image

Merits1) Simple to

implement.2) High payload

capacity.3) Low complexity.

Demerits:1) Vulnerable

corruption.2) Vulnerable to

detection.

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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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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.

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(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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Block Diagram of DCT[2]

secret message

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Encryption

Embedding2D DCT

on each block

8*8 blockpreparati

onCover image 2D IDCT

on each block

Stego image

Embedding information:

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.

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(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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Extracting information[2]

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Stego image

8*8 blockpreparati

on

2D DCT on each

block

Extraction

2D IDCT on each

block

Decryption

Extracted image

Result of DCT

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Cover Image Secrete Image

Output at the receiver side

Cover Image Stego Image

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Advantages Energy compaction. High compression ratio, Small bit error rate Good information integration ability.

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ApplicationIt  is often used in image processing, especially

for lossy compression, because it has a strong "energy compaction" property.

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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 pixelBER= 1 ∑ |image cov -image steg | |image cov| i=0

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(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

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(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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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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ReferencesAnil 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

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THANK YOU

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