Sounds like a joke, right? Well, over at Grand Illusions they’ve explained exactly how to make a print on, yes, a geranium leaf. Here’s how it works:

The chlorophyll in healthy green leaves captures light and uses its energy to join together carbon dioxide and water. The result is the organic compound we call starch. It is the basis of much of the food we eat. Starch is white, but if you drop a small amount of a solution of iodine on it, the starch turns black. So that’s it really. All you have to do is get a plant to produce lots of starch in the right place, then stain the starch with iodine. Don’t let a few details prevent you starting straight away.

The tools and ingredients to produce your own leaf print are pretty basic, so it shouldn’t be hard to make one yourself. Here’s what the resulting leaf print looks like:

As you can see, this process doesn’t produce the most clear and detailed prints, but it’s still a pretty neat photo trick.