I am writing something that needs to verify the practical readability of qr codes which has been painted over.
First thing that comes to mind is to apply Gaussian blur on the image and check if it is readable. Then I could get a “readability score” by doing binary search between blur strengths range [0, n].
I also may do the same with noise, not sure if I should.
Would appreciate if somebody with more knowledge of QR codes help me
The art may be monochrome but the readers interpreting the QR (the part you are supposed to be testing) are almost certainly RGB. If you are not testing from the point of view of a camera reading the image, you are leaving a blind spot, no pun intended, and are not really testing properly.