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Authors: Roberto Caldelli , Francesco Filippini , Mauro Barni

Joint near-lossless compression and watermarking of still images for authentication and tamper location. Authors: Roberto Caldelli , Francesco Filippini , Mauro Barni Source: Science Direct, Signal Process: Image Communication 21 (2006) 890-903 Speaker: Wei Chun, Lin. Outline.

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Authors: Roberto Caldelli , Francesco Filippini , Mauro Barni

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  1. Joint near-lossless compression and watermarking of still images for authentication and tamper location Authors: Roberto Caldelli, Francesco Filippini, Mauro Barni Source: Science Direct, Signal Process: Image Communication 21 (2006) 890-903 Speaker: Wei Chun, Lin

  2. Outline • Introduction • Encoding phase • Watermark detection • Security issue • Experimental results • Conclusions

  3. Introduction • Watermark approaches • Fragile watermarking • Accomplished by inserting within the image a watermark that is readily altered or destroyed as soon as the host image undergoes any manipulations. • Robust watermarking • The watermark is not affected by image manipulation.

  4. Introduction • In this paper, authors use Fridrich’s method, which embeds the least significant bits(LSB) of the host image. • Reason: • its security feathers • its good localization capabilities

  5. Encoding phase • JPEG-LS prediction context Ix: the brightness of the current pixel Ra, Rb, Rc, Rd: neighbor pixels Rd : used only for context modelling (regular mode: Neighbours not very alike)

  6. Encoding phase • Rx = Px + Q R min(Ra, Rb) if Rc ≧ max(Ra, Rb), • Px = max(Ra, Rb)if Rc ≦ min(Ra, Rb), Ra + Rb –Rc otherwise. • E = Ix – Px • Δ= (MAX) differ from original pixel by up to a preset amount • Q E=

  7. Encoding phase

  8. Encoding phase

  9. Watermark detection

  10. Security issue • Multiple stego-image attack • Counterfeiter is making changes that detector cannot reveal or gain knowledge about the secret keys used by the scheme. • Verification device attack • Counterfeiter is making changes also accessing to the verification device and using it to check the integrity of any images he likes.

  11. Security issue • Cover-image attack • Counterfeiter accesses to the image before authentication or uses an estimate of the original which can be performed. Then he has multiple pairs of original and authenticated images. • Chosen cover-image attack • Counterfeiter has the authentication device and he can submit his images to the authentication process to violate the secrets of the system.

  12. Experimental result

  13. Experimental result

  14. Experimental result

  15. Further improvements • Block size 8X16 16X16

  16. Conclusion • Using JPEG-LS can easy to achieve the image compression in this paper.

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