YOu are correct that a gun cannot be imaged behind an actual screen. I am correct that a peice of tinfoil doesn't comprise an actual screen. Go price a shield room, and see how much is for materials, and how much is for labor. Go talk to the crew that's putting it in; you'll see that they travel all the hell over the world putting these things in, because the vendor can't just hire some pick-up electricians and dry-wall types. If the source radiates its EM waves, which reach and intercept the tinfoil, unless the tinfoil is correctly bonded, shielded, grounded, etc, the tinfile will re-radiate. That can be imaged. I do this class of imaging, from signals that are weaker than these, for a living. In fact, we sometimes have to apply attenuation at the front end to stop overload of the amplifiers and signal processors. No, I'm not going to talk about it. Not because I'm a hot-shit keeper of classified information, rather because I'm lazy, or maybe because I'm accustomed to getting paid for teaching? Most of the concepts are discussed in IEEE journals and other sources. You could hand all the open sources, and a few billion dollars, to the Botswanians tomorrow; it would still take them a dozen years to get it working reliably. It's as much art as science. I guess the fancy word is "engineering". You don't know how to do it; so what. I know how to troublehoot and repair it.