Cryptography Reference
In-Depth Information
Spatial-Domain Image Processing Attacks
Several spatial-domain image processing techniques, including image crop-
ping, median filtering, blurring, high-pass filtering, contrast enhancement,
brightness enhancement are done on the watermarked image as shown in
Fig. 11.13. The extracted watermarks are depicted in Fig. 11.14. Except in
the case of high-pass filtering, the robust watermark can successfully survive
with a value of NHS > 0.7. Although the NHS value of the extracted robust
watermark in the high-pass filtering case is a little smaller in our algorithm,
the information conveyed is still recognizable. For the case of image cropping
in the upper-left corner, the extracted semi-fragile watermark can locate the
cropping position. For each case, the semi-fragile watermark can be used to
verify the authenticity of the watermarked image.
(a) (b) (c)
(d) (e) (f)
Fig. 11.13.
The spatial-domain-attacked watermarked images. (a) Image cropping
in the upper-left corner. (b) Median filtering with the radius of 2 pixels. (c) Blurring
with radius = 1.0 and a threshold = 10.0. (d) High-Pass filtering with radius = 10.0.
(e) Contrast Enhancement by 10%. (f) Brightness Enhancement by 10%.
Rotation Attacks
With StirMark, we can perform the geometric attack by rotating the water-
marked image with using different angles. We rotate the watermarked image
by 0.5
◦
and 1
◦
in clockwise and counter-clockwise directions as shown in
