"My understanding is that there's not unshakeable evidence but it's more difficult to dismiss the shroud now," he told CNN's Piers Morgan.
"Some of the scientific evidence has proven that it is, as you say, older, that there are some inexplicable factors, in the stains and the composition of it."
He chose to put the shroud's image on his book cover "because it's simply an icon of Jesus in this generation," he said, whether its origins are proven or not.
"People say, 'that's maybe the oldest picture of Jesus' -- they don't think of it being something that has to be scientifically confirmed," he added.
'Truly mysterious image'
Benedict prayed before the shroud in 2010, when it went on display for six weeks at Turin Cathedral, its first public showing since undergoing a major restoration in 2002. Before that, it was last on display in 2000.
The shroud -- more than 14 feet long and 3 feet, 7 inches wide -- was restored to remove a patchwork repair done by 16th century nuns after the cloth was damaged in a fire.
Thirteen years ago, when Benedict was still Cardinal Joseph Ratzinger, he wrote that the shroud was "a truly mysterious image, which no human artistry was capable of producing."
The shroud is not scheduled to go on public view again for more than a decade, so the TV broadcast represents a rare chance for the faithful to get a glimpse of the famous relic.