A man named Oren Jeffries, an amateur spelunker/photographer, was exploring an unmapped section of Grand Caverns in Virginia conducting photography experiments. He would lay down flat on the cave floor, turn off his lantern, and try to capture photos of things in "cave darkness", or absence of light. One time, he heard something start to approach him from deep in the cave. He became frightened and left. He said he had seen three humanoid creatures.
A few days later, Jeffries and a few friends to retrieve his camera he had left when he had fled before. This is the picture on the film inside.
Here is a brightened version.
For more see this post on Bigfoot Evidence