A Semi-fragile Watermarking Algorithm for Authenticating 2D Engineering Graphics Based on Log-Polar Transformation

A semi-fragile watermarking algorithm for authenticating 2D engineering graphics based on log-polar coordinates mapping is proposed. Firstly, the coordinates of vertices of entities are mapped to the log-polar coordinate system to obtain the invariance of translation, scaling and rotation. Then the watermark is embedded in the mantissa of the real-valued log-polar coordinates via bit substitution. Theoretical analysis and experimental results show that the proposed algorithm is not only robust against incidental operations such as rotation, translation and scaling, but can also detect and locate malicious attacks such as entity modification, entity addition/deletion.