> I mean, it's not that expensive to just take some hi-res X-ray photos of old and new boards of the same make, and compare the trace paths near each component.

> I mean, it's not that expensive to just take some hi-res X-ray photos of old and new boards of the same make, and compare the trace paths near each component. Maybe you can even take a visual diff of the X-ray negatives, if you can get everything lined up tightly enough. There are examples of attacks which cannot be detected by staring at X-rays of components[1]. Now, to be fair they are very advanced attacks but we know they exist. [1]: https://link.springer.com/article/10.1007/s13389-013-0068-0 https://link.springer.com/article/10.1007/s13389-013-0068-0