Detecting small differences in objects

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Hello, I am fairly new to OpenCV library and was wondering what would be the best method find small differences in two images?

What I am working on is a software that detect small differences between two objects, although the compared object may not be fully completed yet, I have made two mock-ups of this and attached it below. Trying to get my program to detect that the object is the same, at the same time detecting that is is different.

I am planning on mainly using matchShapes, but am worried how well it would do with real world images. But I plan to divide my object into parts starting from the bottom, and matching it with the original image.

So what I am asking is if there is a method that I may have missed that you would recommend me looking. any help or ideas would be very greatly appreciated!

This would be the original image:

and this would be the compared image: