Re-Snaps

The idea has been explored by a Russian SF author, who was also a
paleontologist (just can't remember the name). The character, a
geophysicist working in Central Asia, discovers after a blast a cliff made
of coal, protected over millenia by slate. Under the setting sun rays, he
observes a "picture" of standing dinosaurs, "burnt" in the coal. And then,
since he is a scientist, he went on exploring the works of the father of
photography, Niepce de St Victor, who made his first plates with layers of
"bitumen from Judea". After the "snapshot", the images were revealed by
selectively etching the non-illuminated zones with some essential oil. A
few Niepce pictures (made before his collaboration with Daguerre) have
survived.

I can also tell you that highly reflecting haloes are imprinted in coals,
bitumens, asphalts, thucholites,...containing uraniferous inclusions, and
that they are stable over n x 100,000 years. But one should need some time
and an energetic radioactive gun to burn-in the pictures. Pleochroic
haloes in biotite are also very time-resistant, but it takes a few million
years to "write" and the stability of biotite is not guaranteed.

J.J.