do not complicate yourself so much, make a “transparent square” image (with your hands) for example 360x360 or 320x320, in this way they will always be centered. after all the function of changing the image in the hands is with errors, so you will not be able to use it and not doing so does not affect the interactions
Make the hand position exact centre and select the hand. right-click on the hand and select “Reset Pivot”. It moves the pivot centre of the image. You can manually change the pivot point by click and move the pivot mark.