1. Blind detection of image manipulation

• Giorgio Sironi, matr. 764852 Politecnico di Milano - Como, January 12th, 2011

2. Problem statement http://xkcd.com/331 3. Possible solutions

Automated detection of tampering on non-watermarked images

Pixel-based

Format-based

Camera-based

Physics-based

Geometric-based

4. Pixel-based techniques

Detection of cloning,resampling , splicing

5. Format based techniques

Double JPEG , JPEG quantization and blocking

6. Camera based techniques

Chromatic aberration , sensor noise...

7. Physics-based

Light direction(2D or 3D)

8. Geometric-based

Sign manipulations

Assumptions: manual selection, [known font]

9. What is a photograph?

Camera executes a projective transformation ( homography ). We useprojectivegeometry tools.

10. Math background

Homegeneous coordinates: O is (0,0,1)... Or (0,0,2), or (0,0,3). (10, 15) is (10, 15, 1) or (20, 30, 2)

11. Planar homography: 3x3 matrix (linear transformation) 12.

How do we estimate an homography?

13. How do we find the keypoints?

SIFT: feature detection

14. RANSAC: matching of keypoints pairs 15. How do we judge a rectification?

Comparison between (binary) rectified image and world sample(s)

16. It's an arm race Computer programs support projective geometry tools; do humans? 17. References Main Hany Farid, A Survey of Image Forgery Detection (2009), in: IEEE Signal Processing Magazine, 2:26(16-25)Valentina Conotter, Giulia Boato and Hany Farid, Detecting Photo Manipulation on Signs and Billboards, in: International Conference on Image Processing, Hong Kong, 2010R. Hartley and A. Zisserman, Multiple View Geometry in Computer Vision, Cambridge University Press, 2004. D.G. Lowe, Distinctive image features from scale-invariant keypoints, International Journal of Computer Vision, vol. 2,no. 60, pp. 91110, 2004. Minor Prasad S. and K. R. Ramakrishnan, ON RESAMPLING DETECTION AND ITS APPLICATION TO DETECT IMAGE TAMPERING, in: IEEE International Conference on Multimedia and Expo (ICME 2006),, Jul 09-12, 2006, Toronto, Canada, pp. 1325-1328. Micah K. Johnson andHany Farid, Exposing Digital Forgeries by Detecting Inconsistencies in Lighting (2005), in: MM&Sec '05 Proceedings of the 7th workshop on Multimedia and security Babak Mahdian and Stanislav Saic, A Bibliography on Blind Methods for Identifying Image Forgery (2010), in: Signal Processing: Image Communication, 25:6(389-399)Sevinc Bayram, Husrev T. Sencar and Nasir Memon, A Survey of Copy-Move Forgery Detection Techniques, in: IEEE Western New York Image Processing Workshop, Rochester, NY, 2008Nitin Khanna, Aravind K. Mikkilineni, Anthony F. Martone, Gazi N. Ali, George T.-C. Chiu, Jan P. Allebach and Edward J. Delp, A Survey of Forensic Characterization Methods for Physical Devices (2006), in: Digital Investigation, 3:Supplement 1(17-28) 18. Thanks for your attention