Yes, they seem to look for "fingerprints." Your second cover may have interfered with the fingerprint just enough.
I overheard one TSA agent mentoring another on the x-ray machine just a couple days after the iPad 2 was available. The first TSA agent got confused looking at the new iPad2, and the second agent explained how many batteries each had. I overheard something like "iPad 1 had 2 batteries and the iPad 2 had 3, and the batteries should be in these spots." Did you know there were multiple batteries a few days after shipping?
I was impressed. My expectations were low to begin with, but the second TSA agent had legitimate technical knowledge.
Edit: I'm not supporting TSA or saying this is the right approach. This anecdote seemed to support your supposition for how they screened items. I still was impressed an x-ray tech knew the insides of an iPad 2 better than even engadget. Thank you for making your point, though :)
That seems impressive, I agree, and I'm all for giving credit where it's due. But the problem with looking only for "fingerprints" is that you're inherently narrowing your search spectrum. By doing so, you're actually making the job easier for terrorists -- whose goal, roughly speaking, is to move to wherever the spotlight isn't shining.
Bruce Schneier does a much better job explaining this phenomenon than I can ever hope to. But essentially, there's a good argument to be made that totally random searches are superior to fingerprint searches. Terrorists operate on probabilistic scenario analysis. They will only attempt a plot if they're close to 100% sure that they can pull it off, because a failure embarrasses them in the eyes of their sympathizers and would-be financial benefactors. It makes them look like amateurs, and nobody wants to fund an amateurish organization. So even doing something like randomly screening every Nth passenger (where N changes daily) inherently reduces the odds of success by a fixed daily percentage. Terrorists are more scared of dice rolls than they are of fingerprint searches.
I'm no security expert, and for all I know, some combination of random searches and fingerprint searches is the optimal portfolio. I can, at least, understand the logic there, and it makes some sense. But focusing solely on fingerprints creates loopholes everywhere else. And it seems that the TSA has become more and more laser-focused on fingerprints in recent years.
Not long ago some Israeli security hard cases explained how they handle this issue at Ben Gurion. You can probably still find it online somewhere, basically their monitors are highly trained in profiling and they use psychology and hyper profiling to spot potential threats.
I've heard bits and pieces about the Israeli methodology, and I've also heard critiques of its potential for application in the US (mostly, centering on the idea that our population is too big, too diverse, and too spread out to accommodate the training and consistency of the Israeli program).
Whatever the case, one thing does seem fairly clear: that the Israeli investment in people, rather than machines, seems to be paying a good dividend. And I'm tempted to say that we'd be better off staffing airports with better people and slightly older / less intrusive machines, rather than cutting-edge machines and bottom-of-the-barrel staff.
I overheard one TSA agent mentoring another on the x-ray machine just a couple days after the iPad 2 was available. The first TSA agent got confused looking at the new iPad2, and the second agent explained how many batteries each had. I overheard something like "iPad 1 had 2 batteries and the iPad 2 had 3, and the batteries should be in these spots." Did you know there were multiple batteries a few days after shipping?
I was impressed. My expectations were low to begin with, but the second TSA agent had legitimate technical knowledge.
Edit: I'm not supporting TSA or saying this is the right approach. This anecdote seemed to support your supposition for how they screened items. I still was impressed an x-ray tech knew the insides of an iPad 2 better than even engadget. Thank you for making your point, though :)