What else causes this pattern to change? Time, or light, perhaps?
to quote this thread, which someone seems determined to bury for some reason
https://news.ycombinator.com/item?id=39424773
"The issue not mentioned is one I've encountered in other similar projects which is false negatives cause by "creep" in plastics and general thermoplastic movement. We had a near-UV scanner that could map the surface of a test object (sensitive circuit boards) down to a few wavelengths, but it was too damn accurate. Go back and scan the same object a week later and stuff (like solder joints) has moved naturally. That doesn't work when things are in transit for weeks with vibrations and temperature variations"
People may be downvoting the top message because it contributes nothing. It doesn't require some nebulous malicious actor somehow trying to keep you down.