What we see as evidence
I'm completely fascinated by what Karin Knorr-Cetina calls "technologies of representation" - where scientists use object traces (like photos) to stand in for the objects themselves. This sort of scientific practice requires specific technologies - such as telescopes or cameras - to remove real-world constraints of location and time, and thus allow analysis of the outside world to proceed inside the lab. For example, Knorr-Cetina discusses how astronomy changed from being a field science practiced only at night to an imaging science where astronomers could observe pictures of celestial phenomena anytime, anywhere. In addition to this portability, image processing may include the addition of colour "to enhance an object's detail or to visualize what ordinarily could never be seen by the human eye". In these processes of representing nature, the scientist too becomes an instrument: one who recognises and decodes the proper signs in order to 'discover' scientific fact.
This tension between image and interpretation was also at play in the early days of photography. For example, in 1852 Marcus Root described a daguerreotype as a "literal transcript" that "will serve, perhaps, even better than its living original". At the same time, he considered it a "monstrous absurdity to regard the art itself as a mere process of mechanical transcription". In other words, if photographs were to be considered an original art form then a photographer would have to be more than "a mere mechanic".
Another example comes from Thomas Thurston's study of photographic evidence in 19th century American courts, where he notes:
Sound familiar? Today, we argue about the reliability of DNA evidence, suggesting that it is only as good as the people processing it. I also think about how much of our current scientific knowledge is at a distance - molecular biology, particle physics, nanotech etc. all deal with things invisible to the human eye - and I think we'll increasingly need to critically understand the relationships between the world around us and our representations of it.