German professor named Johann Schulze accidently stumbled upon the first photosensitive compound. What's a photosensitive compound? Well, it's a material that changes when it's exposed to light. In other words, it's sensitive to light. In Schulze's case, he was experimenting with different types of silver salts. He observed that certain salts—like silver nitrate and, urn, silver chloride—darkened when exposed to light. You all see why that’s important, right? I mean, if you have a photosensitive material, there's a chance you can capture an image on it. So ... Schulze didn't end up doing anything with his discovery. But it inspired a lot of other scientists. For example, throughout the 1790s, an English photography pioneer named Thomas Wedgwood covered different materials with silver nitrate. For example, he put the silver nitrate on pieces of leather and glass, stuff like that. Anyway, he then placed these materials inside the camera obscura and projected images onto them. What do you think the result of this was? Of course! He was able to create a photograph on the surface of the material. But there was a catch.. Wedgwood didn't have a way of preserving, or fixing, the image. So when the piece of leather or whatever was exposed to light later, the entire thing would turn dark, and the photo was lost.