11 December 2010
Photos and metadata
For anyone who may be unfamiliar, metadata are data that describe other data. A digital camera picture presents a good example: the data represents the image itself, and metadata include other information like when the picture was taken and with what exposure. I've recently been putting a number of slides through a digitizer, which has reminded me that only limited and coarse metadata came along when film was developed. There was usually a stamp indicating the month when the film was processed, which clearly demonstrates that a picture wasn't taken later but doesn't say anything about how much time elapsed between the exposure and its development. There was also a sequence number designating a picture's position in a roll, but it may not always be obvious which roll it belonged to if several rolls were processed at the same time. (If my samples are indicative, different processing labs provided stamped annotations that differed in detail.) It shouldn't usually take much guesswork or puzzle solving to assemble a sequence, but having to do so contrasts with what newer technology provides automatically. As for exact time data, it's not normally available, except if there's an associated handwritten note, a clock in view, or (interesting special case) the image depicts a specifically noted event like an eclipse.