[drc]

Copies of negatives don't have the same image quality as the original. Some copies of negatives are quite rough. So looking at the quality of the image on both the negative and the paper photograph is part of determining if it's an original.

Some old photos have images that are so detailed and crystal clear, they had to have been made from an original negative.

The only problem is a photo can be original yet was shot out of focus or at a great distance. Original sports action shots can be grainy or slightly blurred. If I had a photo that I knew was from the year, but the image was rough so I couldn't say for certain the image was made from the original negative, I'd all it vintage 1933 (for year example) and not say whether or not it was original (fromt he original negative). If you don't know, you don't make it up. And for the collector, the old age itself has value.

The 1913 T200 Fatima team cards, which are photographs, are obviously vintage, but the images appear second generation. So that's an example where a photo image isn't original but the photo is vintage. As they were mass produced, real photo baseball cards are more likely not to have been made from duplicate and copy images.

The negatives themselves can be dated roughly as physical objects. For example a 1910 negative would be glass, and an 1870 negative would be glass with a different thickness and cut. Modern slides, which are also used to make photographic prints, commonly have the date of manufacture printed on them-- so they're easy to date.

One thing to realize is that age itself is part of a photo's value. Say you find an 1860 cabinet card of Abraham Lincoln and someone tells you the image is second generation. As President of the United States they were making lots and various kinds of photos of him, and the images were sometimes copies of other images. You may be bummed the images isn't first generation, but the cabinet card will still have value due to it being from 1860. It's still a Civil War era antique.