'Phantom' x-ray weapon

If full-size x-ray photographs of various dangerous items are printed on paper using lead-based ink, then whenever one of these sheets is inspected with an X-ray machine, it's indistiguisable from the dangerous item itself. Yet the "virtual object" would be flat for convenient storage or mailing. Similar items are commonly used for training purposes in medicine and are called "phantoms," but they're usually 3D rather than flat.

If "phantoms" are flat, a kit of many hundreds of different x-ray sample weapons could be stored in a ring binder, whereas the samples of actual weapons would require a large amount of shelf space. With flat phantoms, every airport could have its own inspector training center with a variety of "real" objects for students to detect within cluttered luggage.

For "suprise inspection" of x-ray machine operators, where weapons to be found are placed into luggage, no embarassing situations occur if they lose track of that luggage. Only a nondescript piece of cardboard ends up on the flight.

Also, the kit could contain very realistic images of certain objects which would be otherwise unavailable for training purposes because of their expense, danger, or illegality (e.g. live ammo, plastic explosives, blasting caps, military weapons, etc.)

Also, as new types of smuggled weapons were discovered by authorities, phantoms of each new type could be distributed to all airports for training purposes within a matter of hours.

For chemically-selective x-ray machines, certain parts of the phantoms could be printed with inks containing those chemicals. E.g. print the image of blasting caps with silver ink to imitate the silver-based high explosive.