1. Fault Resilient and Compression Tolerant Digital Signature for Image Authentication
Der-Chyuan Lou and Jiang-Lung Liu,
IEEE Transactions on Consumer Electronics, Vol. 46, No. 1,February 2000, pp.31-39
Advisor ：Dr. Chang, Chin-Chen
Reporter：Lee, Jiau-Yun
Date ：2003/3/25

2. Outline Introduction The Proposed Method Feature Extraction
Feature Comparison
Image Recovery
Experimental Results
Conclusions

3. Introduction Image authentication is becoming important.
The study categories of Image authentication:
Digital watermark---sellers
Digital signature---buyers
The criteria of fault resilient and compression tolerant scheme.

4. The Criteria of Fault Resilient and Compression Tolerant Scheme
Any legal receiver can authenticate the ownership.
It should be detected when the image is tampered.
The modified portion should be located.
The hash result should be small and robust.

5. The Proposed Method Digital signature generation: Feature Original
Extraction
Encryption
Original
Image
Digital
Signature
Sender’s
Secret Key

6. The Proposed Method(cont.)
Verification and recovery:
Received
Image
Decompression
Feature
Extraction
Feature
Comparison
Digital
Signature
Decryption
Feature
Reversing
Sender’s
Public Key
Image
Recovery

7. Feature Extraction---Steps
Original
Image
Block-means
computation
Block-means
Quantization
Encoding
Image
Feature

8. Feature Extraction---Steps(cont.)
Steps can be formulated as:
Original map: Io
Block-means map: IM
Quantized means map: IQ
Encoded map: IE
Transformation function: f

9. Feature Extraction---threshold
Block-means
Quantization
Original
Image
Block-means
computation
Encoding
Image
Feature
Compression
& Decompression
Corrupted
Image
Block-means
Quantization
Difference
Computation
threshold
Compression
ration

10. Feature Comparison The procedure of feature comparison:
1.Create a temporary map of the same size
as feature map and assign white color.
2.Find the difference between two features.
3.If the difference is large than the threshold, then mark it with black
4.If no black-marked in the temporary map,
it is authentic.

11. Image Recovery Replace the intensity of black-marked blocks.
There will possible exist some edges between blocks.
Smoothing algorithms:
8 neighbor blocks must be recovered while the black-marked block is recovered.

12. Experimental Results
(a)original image (b)map of block-means (c)quantized
(256*256) (32*32) block-means(32*32)

13. Experimental Results(cont.)
a tampered
image by
removing
“U.S. AIR
Force”
the detected
result.
recovered
image by using
received
image-feature.
PSNR= dB
retransmission 5%
PSNR= dB

14. Conclusions The proposed image-features are compression tolerant.
The threshold for compression tolerant property is user-defined.
The proposed image-features can recover the modified portions.