Interesting article in The Tennessean by writer Frank Daniels III looking at the career of inventor Nicéphore Niépce, credited with making the first photograph.
He apparently made some photographs around 1816 and developed the first photogravure process in 1822. His photoengraving of Pope Pius VII is considered the first photographic etching; the etching was destroyed when he tried to print it. He experimented with several light-sensitive chemicals and settled on bitumen dissolved in lavender oil. He spread the mixture on a sheet of pewter and used a camera obscura to capture an image. He called the process heliography, “sun writing.” Niépce began working with Louis Daguerre in 1829 but he died in 1833 before their processes were perfected. Daguerre eventually perfected his process, Daguerreotype, in 1839. It became the first successful photographic process.
The Wikipedia entry on Niépce’s oldest surveying photograph, “View from the Window at Le Gras,” made in 1826, says experts estimate the image required an exposure time of at least 8 hours, and possibly “several days.”