Thanks for taking the time to try that out and sharing it! Our problem is with defects on the order of 50 to 100 microns on bare boards. Defects that only a trained tech with a microscope can see - even then it's very difficult.
Seems like a exciting problem. Hope you get tools in the future which can solve it well.
It looks like there could be a lot of potential here for learning/repair/debugging/reverse engineering. Really cool application of this stuff!
Generally this is called automated anomaly detection.