Hmm. I'm partially playing the devil's avocado here, but I think to me the element of "the exact same glass plates" isn't as big a factor as it is to you. After all, the image you linked (lank? lunk?) to is at least one generation removed, but my eye takes it as a kind of "authentic proxy" for the plate, and I'm comfortable with taking for granted that the scan represents the plate (maybe through the intermediary of a print, I don't know) in much the same way that you and I are both comfortable accepting that the plate represents the event.In an example that 'blanksy' and I have toiled over several times, the reason that Alexander Gardner's glass plate negatives of the Hanging of the Lincoln Conspirators are so breathtaking is not that they tell us those four souls died at the end of four ropes. We already knew that from the history books before ever visiting the Library of Congess, donning white cotton gloves, and being handed the actual glass plates to hold up to the light and gaze at.
No, the reason they are breathtaking is that while looking at them we suddenly come to realize that those fragile plates in our hands were, at the moment those four souls finally hung, physically present inside of Mr. Gardner's wet-plate camera, situated on the second floor of that building overlooking the gallows, only about twenty yards from the doomed prisoners, on that long ago March afternoon. And now we are holding those exact same glass plates in our hands 148 years later thus affirming, via these singular first generation objects, that those events did, in fact, really take place.
But obviously there are all kinds of artifacts of the illusion that is photography at all these stages---I mean, the real people hanged were three-dimensional and in color, right?---and we are drawing distinctions about what we do and don't accept as a level of removal that doesn't impair "credibility" or "authenticity", not between "really the same thing as the actual event" and "merely a representation".
Well, it all depends on what you call "reality". We all have legions of bad photos that made us say "aw, hell, that's not what it looked like at all", right? (I've got a nice one of a five-year-old kid and his dad, only I shot at *just* the wrong moment and the slide gives the very convincing illusion that the kid was giving me the finger! Not at all a semantically correct representation of the "reality of the original events", except in the tautological sense that those photons *did* arrive at the film plane.)The negative bears silent witness to the reality of the original events rendered upon it. That's what photographic provenance means to me, and why it is so crucially important to me that a real photograph needs to possess it.
And we accept certain distortions like motion blur and out-of-focus areas as being somehow accurately representational, perhaps because they create a similar impression to things that happen in our brains when viewing reality. But that's not really "silent witness", it's "lead the viewer to the same conclusion by different means", and those techniques can be used in ways that seem "accurate" (shallow DOF to draw attention to the subject of a portrait) or "inaccurate" (tilt-shift faux-miniatures). So your line is a little too clearly drawn for me, a little too much of a demand for rigorously defined areas of doubt and uncertainty.
There's something about a distinction between art-photography and documentary-photography here, too, though I can't put my finger on what it is in a succinct way. Your concept of provenance seems to me a bit specific to the documentary world, in that it leads you to use a lot of words like "real" and "original" that seem to privilege the accurate representation...whatever "accurate" means, which in itself is a hard philosophical question, n'est-ce-pas?