There is actually a development step possible to speed up leaf photography.

The first step is a long exposure with a high contrast negative pressed to the leaf. Then the leaf is picked and boiled in alcohol (care, fire hazard) to dissolve out the chlorophyll. Next is a soak in a dilute iodine solution. A blue toned image appears.

What happens is that the illuminated portions of the leaf carry out photosynthesis which culminates in the production of microscopic starch grains. The iodine-starch complex is the blue stuff making up the image.