It turns out that in classical Rome (and possibly earlier in Lydia) the means for refining gold from electrum was to smelt the electrum with salt to oxidize the silver to silver chloride. (The modern nitric-acid process wasn’t possible until nitric acid was produced; it was available by the 13th century, but wasn't available in classical Rome.)
Silver chloride is one of the silver halides used in photography; it can be used by itself. Silver chloride plus gelatin is by itself adequate to produce negative prints on paper (or papyrus) given enough light and time.
The Romans had gelatin, too; the widespread use of hide glue dates from Middle Kingdom Egypt. So they had the materials technology necessary for photography. We could be looking at Julius Caesar’s hobby pinhole landscape photographs today if they had known about the properties of the materials they had at hand.
(Actually, I’m not 100% sure that the collagen in hide glue is sufficiently similar to gelatin; gelatin is collagen hydrolyzed either simply by boiling or more quickly with acids, bases, or proteolytic enzymes.)