MASTER THESIS Video Watermarking - Computer Graphics Group ...

5.4.9 Collusion
The collusion attack consists in combining several differently watermarked
copies to destroy the watermark.
The attack is simulated in the plugin itself during the embedding process.
There are two types of collusion attacks, thus two modes of the simulation has
been implemented:
Collusion by averaging
This mode is based on averaging of corresponding pixel color samples of
participating copies. In case of block and coefficient methods, it may cause
appearance of non-zero coefficients where they have not been and vice versa
resulting in invalid detection of watermark element values. In case of noise
method, the attack causes averaging of the noise patterns. Lesser impairment is
expected in this case because the average pattern contains all the single patterns
which are statistically independent.
The simulation takes place in the embedding process. Required number of
watermarks is generated. The same number of differently watermarked versions
is created when watermarking single macroblocks. Then, the average
macroblocks are estimated.
The results in Table 12 are average values of probabilities given by the
detector from the corresponding number of copies. The numbers of copies are
listed in column named #C.
Table 12: Collusion by averaging test results
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