The original pictures here were colour slides - a silhouette of
a Red Arrow Hawk jet on one slide, and a close up of some barbed
wire against the sky - specially taken.

Both slides were mounted together in the same mount. This can be
used as it is, but the judge can be fooled by re-photographing
the sandwich to create a master slide. 




I have a slide copier that fits onto the camera in place of a
lens - an SLR of course - and allows some zooming and cropping.
there are all sorts of ways of lighting the copy, but something
akin to daylight is the best bet, so why not point the assembly
at a blue sky / I've also done tests with a flash fired directly
into the copier, and in some cases, auto 'off the film plane'
flash exposure works well.

In this case the film was a black and white one.