What defines an original photograph?

I think I would define a photograph as a positive print that you can hold in your hand and look at, a digital photograph is the same except it's from a digital image rather than a negative. I would not call a negative a photograph - it's a negative and nothing more. So, an original photograph is the first (successful) print that is made from the source (negative or digital image), but all subsequent copies made from the same source would probably be called duplicates. While a digital photograph only exists inside a memory card or computer, I would define it technically as an image as it is potentially no different from a scribble made in Photoshop or whatever.

There's also the other meaning of original - unique, so if one person takes a photograph of something and then another person comes along and photographs the same thing in exactly the same manner, who has the original photograph? Very tricky to decide! If it's obvious that the second person copied what the first person did then I would say the first person did the original photograph, but that's just what I think.

In the old days, photographers used all sorts of techniques in post production (pushing, dodging, and burning come to mind). To the greats, like Ansel Adams, this was even an integral part of photography. And then there's the choice of paper, the frame, etc...
I agree with that line of thinking, so I'd say that with film and digital alike, the captured shot is just raw material - it's the final result that matters.
With art photos, who even cares how much was retouched. It only becomes an issue with photojournalism, etc.
As for originals vs. copies (?), when you make 100 prints of the same picture, you've got 100 reproductions.

the original is the negative.

just like the in the digital era the original unedtied file straight out the camera is the original.

an original print is usually a limited edition of high quality, often printed by the hand in a darkroom or on a printer owned by the photographer.

it is the image that is the original and not the photo itself. so in the old days the first positive was the original now with digital the origianal is on the card not the print out

RAW files are considered kind of like a digital negative, which is un-edited and un-interpreted.

Good question. The real answer to your question might emerge after you read the series of answers that I hope you will generate.

I try to keep a file of "uneditted images" so that I can always go back to square one if I want to. I guess they are "original."

I have read a little about memory cards that can not be altered that are designed for police work. There is some type of encoding that makes it impossible to resave an editted image to the card. I think you can get around that with a password, though, if you are authorized to do so.

1 that hasn't been done before