We must not misinterpret Susan Sontag and the quotation from "On Photography". I believe that it is wrong to look at photographs as either, only copies, or only interpretations, of the world - they are a little bit of both.
On one hand, taking a photograph is a pretty straightforward process, during which an image is burned onto light-sensitive photographic film. The subject of the image must exist physically before the shutter ever opens. It is obvious that the photographer cannot capture an image of a subject that does not exist. Therefore, the only attributes that the photographer can change before capturing the image, are constrained by the capabilities of the camera equipment that is used, and the environment to which the subject belongs.
On the other hand, a painter may paint an interpretation to which he can add infinite characteristics with the power of the imagination-driven brush. We may conceive of photographs as closer interpretations of reality than paintings, because we perceive photographs as frozen realities, or at least images of an infinitely variable world. To be quite frank, 99% of the time photographs are highly realistic in terms of what they depict, thus they are evidence that, whatever they depict either existed at the time, or still does. Susan Sontag once wrote:
If it is correct, the above further proves the assertion that photographs indeed form evidence of the reality which surrounds each one of us. So, what is this "other reality" that Jerry N. Uelsmann mentions in the opening quotation? I believe it refers to the interpretation of reality. As we perceive and interpret the world around us, we are perceiving and interpreting reality. Everyone's perception and interpretation differs, therefore everyone's reality also differs. By using the word interpretation, I mean to say translation, or decoding. So, as we all translate reality differently, we also capture reality differently. Hence, the notion of photographs being both copies, and interpretations at the same time, can definitely be valid.
Interpretations are copies of the same reality but all belong to a different point of view - not always the physical point of view, but also of the imaginative. So, as our retinas all receive the same message per se (angles or lighting difference might make a message seem different), how this is translated, decoded or interpreted, makes the more radical changes to how or what any of us actually perceives. We enjoy reproducing our own translations, and we do this in many ways. One of the ways is by taking a photograph - or in some cases a few thousand. It is we who perceive, making reality, a reality.
Introduction To Media Theory ~ University of Wales, Aberystwyth