When you buy enough "junk" that just looks old and or unique you'll eventually hit jackpot, I'm really not sure that the guy who bought the picture knew exactly it's value or it's historical significance, he just might had enough experience to estimate that it's more likely than not worth more than 2$ and got really really lucky.
An original old-western picture could probably get more than 2$ on Ebay and the likes as just decorative art so even without it's historical significance it could've been purchased as an "investment".
1) We end up with a junk piece of furniture that sits in our garage for months while she tries to either sell it for a few bucks or makes a run back to the thrift store to drop it off (majority of the time)
or
2) She ends up finding a piece worth hundreds (sometimes thousands) that make it all worth it. She recently found a Paul McCobb table she restored and sold for 700 dollars that she bought for $15 (small % of the time but worth it)
Kinda sounds a bit like venture capital...
"But does it scale?" :-)
[1] https://en.wikipedia.org/wiki/Taxila [2] https://en.wikipedia.org/wiki/Nalanda#Decline_and_end
The other, brighter side of this coin is the many remarkable rediscovery stories, like that of the Archimedes palimpsest [3] in the 1990s and Indian statesman Chanakya's 3rd century BCE manuscript 'Arthashastra' [4] in the 1900s.
[3] http://www.archimedespalimpsest.org/ [4] https://en.wikipedia.org/wiki/Arthashastra
Many of the documents found at Nag Hammadi were burned before anyone read them. Among the unburned was a copy of Plato's Republic (not an original, but still).
https://en.wikipedia.org/wiki/Nag_Hammadi_library
Reading these makes me wonder what other interesting written interpretations of various religious figures were burned out of existence.
https://upload.wikimedia.org/wikipedia/commons/c/c2/Billy_th...
I'm not anything like an expert, but looking at the enlarged portion, he was the one who came to mind.