radial image perceptual hash

Radial Image Hash

paper:Robust image hashing based on radial variance of pixels

work flow:

1.cvsmooth

2.convert cartesian coordinates to log polar coordinate

3.get the varience to captures image discontinuities

4.get radial variance vector

5.do DCT transfrom

6.get the most important DCT coefficient

7.generate hash value

代码实现比较容易，opencv提供了很多方便的函数，比如cvLogPolar，cvSubS， cvReduce，cvDCT