A semi-fragile watermarking algorithm for authenticating 2D CAD engineering graphics based on log-polar transformation

Copyright violation and illegal manipulation of digital data have been acute challenges for many sectors since the very same set of enabling techniques for generating and processing digital data started to emerge. Although traditional protective methods, such as encryption and digital signatures, have been in use for decades, their inability to provide protection after decryption and locating tampering has prompted the development of digital watermarking. In this paper, a semi-fragile watermarking algorithm for authenticating 2D CAD engineering graphics based on log-polar coordinate mapping is proposed. Firstly, the vertices are divided into groups, and for each group, the vertices for carrying a watermark are mapped to the log-polar coordinate system. 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 global operations such as rotation, translation and scaling, but can also detect and locate malicious attacks such as entity modification and entity addition/deletion.