mse of dct blocks

I have original block and attacked block with some attacks like jpeg, now I compute DCT of each blocks and I divide each DCT blocks to 3 area low, high and middle frequency like following image. now I want to calculate MSE for each part separately and finally choose one part with maximum MSE, but I think the value of frequencies in each part can effect on final MSE of each part! how can I do it and independent the MSE from frequency value?

[Walter Roberson]

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