If you follow the link to the Kagins website, it says "Kevin Costner will narrate and produce the two-hour documentary for National Geographic Channel, covering

If you follow the link to the Kagins website, it says "Kevin Costner will narrate and produce the two-hour documentary for National Geographic Channel, covering Western Americana enthusiast Randy Guijarro’s odyssey to authenticate this unique photograph". So details of the verification process are being withheld in order the make the documentary more appealing.