why Invariant moments are slightly diffident for the same image

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it is mentioned as Hu-moments are invariant from scale, rotation and orientation. But when i compared the Hu-moments by using same image with different sizes, i got slightly different values.

i get image with 100,75(height,width) at first time and then same image with 200,150(height, width) at second time.

can someone explain the reason for that? plz help.

thank you