The world's first photograph required an exposure time of how long?

French inventor Joseph-Nicéphore Niépce is credited with making the first permanent photograph in 1826 using a camera obscura and a pewter plate coated with bitumen of Judea (an asphalt derived from petroleum) that was exposed then washed with lavender oil and petroleum to remove the bitumen not hardened by light, achieving the image above.

The amount of time that it was exposed is disputed, however. It was long suggested that the exposure time was 8-9 hours, however, researchers dedicated to preserving the history of photography studied Niépce's notes and have since reported that it would have in fact taken several days of exposure to capture the image.