Which Transformation, Or Similarity Metric, Is Rotation, Shift and Scale Invariant? I have an algorithm to to detect copy-move forgeries in images. I used block matching to detect regions of an image that were forged with copy-move forgery and highlighted the alleged areas. For block matching, I took the DCT of each block and normalized with an extended 16x16 quantization matrix. 

The problem: 


this approach does not work if the copied region is rotated or scaled. 


My question: 


What transformation/similarity metric would be invariant to rotations, shifts, and scaling? (Alternatively, is there another method available for solving this problem?)
Additional points if the method is already available in MATLAB. 


Thanks for the help.

The code for this project is available here: copy-move forgery detection. 

Edit: I am aware of the Radial Gradient Transform, but I don't think it is invariant to all three.
Use a methods called Error Level Analysis (ELA). It can solve your problem as many forensic applications use it to detected doctored reigns in digital images.