I don't work with customs, but I have done work with computer vision and scanning technologies at near the cutting edge.
From my perspective, the technology is not there to make it cost effective to worry about that sort of thing, and there are too many things for any random individual doing inspection to keep in mind. Too easy to change, too much work to vet it working in the CV model, etc.
If you think about what x-ray scanners look at, they don't see the graphics on packaging or things written on them, and we don't have other types of "see-through vision" that would let them see this without opening packages, and the sheer volume means they need to identify things without opening and inspecting whenever possible. What they do see, however, is density and can determine the atomic number of what they're scanning.
That being said, it's easy to just not post pictures or codes if the vendors prefer it, and that is certainly the case. Drug dealers tend to be paranoid and why piss off the people with the supply?