To get past the awkwardness of the uniqueness thing, I retroactively declare that we are looking for the unambiguously unique, physical, original object, which indeed in part represents a human, was created in a known year, etc. Clue: not many people have seen the original, and I can find no information about whether it even still exists.
Is it the photograph of the Tiananmen Square protestor and tanks?
Hail Radox! I note that the aforementioned Wikipedia has a "List of photographs considered the most important", though I'd think we're a few weeks away from recourse to that.
What springs to mind is either the photo of the Montparnasse train crash, although it doesn't have anybody on it, and the Conan Doyle 'fairies at the bottom of the garden' photo, but that has a whole person, not part of one, so I'm going to ask if the photo was taken before 1930?
[P] Not Miss Napalm 1972. Remember, this was not created to be a record of something. [RtG] Not a record sleeve, or anything else to do with "records" in that sense.
Sorry, I missed Boolbar and Simons: [B] The person's face is visible. (Knowing murmurs from the audience.) [SM] Not scientific (but approving murmurs from the audience).
[SM] It is not, but that's on me for not having any previous knowledge of a landform called Lord Hereford's Knob. [b] It...certainly protrudes from it, but no, more localised than that.
[blamelewis] Aye! It is indeed Arthur’s Seat. Take these bagpipes and a sturdy pair of hiking boots, and either play to the wind or chuck them off the top, I guess.
[Tuj] Not aware of any of them going by Arthur. [Raak] Not an individual. [Projoy] 25 more guesses. [Simons] Possibly, but it's not a regular part of the human diet. Also lots of people would be quite cross.
[RTG] No! [g] No! or, by a certain reading of that sentence, Yes! *the audience mutter amongst themselves about different meanings of the word 'act'* [R] No!
[B] No! [R] I think No! is the clearest answer here, though there's certainly an interpretation of that question which could yield a Yes!.*the audience, clearly a pleasantly diverse group of thinkers, politely interlocute about the meanings the words "assembly" and "together" can have*
[R] No! [P1] No! *a large proportion of the audience goes ooh!* [SM] No! Either I've forgotten it, or that's before my time... [P2] No! *a smaller number of oohs from the audience, but also some eye-rolling ;)*
[C] No! *a few audience members over-excitedly swoon* [SM] No! [P] No! So the answer would be... "not the answer"? I think what I've set is much more straightforward than that, but time will tell :D
Just passing through on my way to save something or other, and understanding the absolute necessity of the internet to satisfy this question, how about the list of all words used in this game as AOTCs?
[S] No! [P] Yes! Because... [SM] YES! *balloons and streamers shower down from the ceiling onto the audience as Simons is handed the very AOTC that's been being hunted, in one of its many (but typically mineral) forms*