At the advent of photography, most people didn’t believe it was possible for a photograph to be manipulated. Thus, when they saw visual “proof” in a photograph, it would bypass their normal filters for determining what is or is not believable.
As people have become more familiar with how much photographs can be manipulated, and as the tools for doing that manipulation have become more powerful and accessible, that special status that photography once enjoyed has faded away. It isn’t that photographs are inherently distrusted, but just that they’re no longer inherently trusted. Today, I would guess that a photograph carries only slightly more inherent trust than the written word—and then only because people know it is still much harder to convincingly fabricate a photo than it is to fabricate a story.