For most of its history photography had a problem of status. If an image can be reproduced endlessly, in what sense does an "original" exist? That question kept photography out of collections for decades, leaving it the role of document.
The reproducibility problem
The difficulty is real, not rhetorical. A painting is a unique object: the hand that made it and the work coincide. A negative is a matrix. From one negative you can pull ten copies or ten thousand, all legitimate, all identical.
Until the 1960s that was enough to exclude photography from the art market. Value in that market has always rested on rarity.
The solution was a convention, not a technology
What changed things was not a technical discovery: it was the adoption of a rule borrowed from printmaking. The author declares in advance how many copies will exist, numbers them, and undertakes to make no more.
It is a convention, and it works for the reason any convention works: because it is verifiable, and because anyone who breaks it loses credibility. From that point a photograph could have a declared rarity, and therefore a price that was not arbitrary.
What makes a print "original"
In current usage, an artist's print is one where the author controls the passage from negative (or file) to paper: the choice of support, the contrast, the crop, the treatment. Two prints from the same negative made twenty years apart, on different papers, are two different objects — and the market treats them as such.
From this follow the three questions that matter when buying a photograph, and they are always the same: what paper, what process, what edition size. The guide to editions and print runs works through them in detail.
The advantage for buyers today
That photography entered the art market late is, for a buyer on a contained budget, good news. The entry level stays far below that of painting, at equal quality and equal seriousness of the author, simply because the history of photographic collecting is shorter.
You can see it in our catalogue: the real per-medium figures are in the photography price guide, and the available selection sits in art photography and black and white.
What to look at in a print, in practice
Beyond the paperwork, the eye trains on three things. The blacks: they should hold detail, not close into a single mass. The highlights: they should not be blown, that is, pure white with no information left. The paper: baryta, cotton, gloss or matte change the result more than the subject does.
If those criteria interest you, they cover the same ground as what to look for in art photography.