Information hiding in stationary images
staff corporal Piotr LenarczykMilitary Uniwersity of Technology Institute of Electronics and Telecomunication
Watermarking
„Digital image watermarking means embedding information into image in such a way that it is imperceptible to a human observer, but can be easily detected by special computer algorithm.”
Ingemar J. Cox
Applications of watermarking
• Owner Identification• Proof of Ownership • Copy Control• Device Control• Broadcast Monitoring• Content Authentication
2-Dimensional Discrete Cosine Transform DCT 2D
M,N = 8
m,n – discrete index of pixel position
k,l discrete index of DCT coefficient
DCT 2D Basis Functions
Basis functions matrices of Discrete Cosine Transform for block 8x8 pix
2 dimensional Discrete Cosine Transform coefficients
Standard quantization matrix used in JPEG algorithm
16 11 10 16 24 40 51 61
12 12 14 19 26 58 60 55
14 13 16 24 40 57 69 56
14 17 22 29 51 87 80 62
18 22 37 56 68109
103
77
24 35 55 64 81104
113
92
49 64 78 87103
121
120
101
72 92 95 98112
100
103
99
Q=
162 162 162 161 162 157 163 161162 162 162 161 162 157 163 161162 162 162 161 162 157 163 161162 162 162 161 162 157 163 161162 162 162 161 162 157 163 161164 164 158 155 161 159 159 160160 160 163 158 160 162 159 156159 159 155 157 158 159 156 157
1283,5 4,77 3,24 -0,2 0,25 -0,55 -4,59 5,647,95 -0,79 -4,93 1,96 2,98 -3,8 3,32
-5,03 -0,3 -1,55 1,72 -0,68 -0,45 1,85 -2,22,26 1,14 1,7 0,92 -0,76 -1,37 0,21 1,14
-1 -1,15 -0,34 -1,36 1,75 1,12 -1,48 -0,671,21 0,46 -1,8 -0,11 -2,01 0,71 1,69 0,76-1,7 0,26 3,1 1,64 1,63 -2,25 -1,2 -0,91,33 -0,42 -2,38 -1,59 -0,88 1,97 0,55 0,65
Matrix A represents block of 8 x 8 pixel values
Matrix B represents DCT 2D calculated on matrix A:
A =
B =
0,5523,55
Original image
Watermarked image
Original picture Watermarked picture for scalling coefficient k=23
Watermarked picture for scalling coefficient k=3000
Algorithm CharacteristicSupported formats BMP 16, 24 bits
PNG, JPG 24 bits
Minimal picture size [pix x pix] 256 x 256
Data payload [bits] 130
Error correction BCH – correction capability of 14 bits
Redundancy of embedded information At least four times
Method advantages Robust against multiply rotation of 90 degrees
Robust against high-pass filtering
Robust against picture distortion like text embedding, painting
Robust against lossy JPG compression - approximately 70%
JPEG format popularity
Program execution time [sec] BMP format, picture size 400 x 400 pix
Coder - 0,12
Decoder - 0,07
Program execution time [sec]JPG format, picture size 400 x 400 pix
Coder - 0,63
Decoder - 0,29