I am cross-posting this to the Live Plant Image email list in addition to tdwg-content because this is a subject that was previously discussed there. However, as this is part of the public review of the draft Audubon Core TDWG standard, I would request that you reply only to the tdwg-content list, so that any additional discussion will take place there for the record. If you aren't on that list and would like to reply, please send your responses to steve.baskauf@vanderbilt.edu and I will post it for you.
This subject came up as part of a comment on Audubon Core from Andréa Matsunaga:
"In iDigBio (http://tinyurl.com/MISC-Media), some people have expressed the desire to have information about the magnification being used (to have a rough idea of the size of the object, potentially from data that is automatically retrieved from the capturing device) as well as the real world size depicted by a pixel (for the purposes of allowing one to make measurements on the image; this would require one to have a scale on an image and perform some arithmetic). Would it be possible to add such terms?"
There are terms in the SpatialMetrics terms (section 9.1) of the MIX vocabulary (http://www.loc.gov/standards/mix/ ) that can encode this kind of information. However, I would be interested in opinions about whether expressing this kind of information is a narrow need that is outside the scope of a fairly broad standard like Audubon Core or if the need for such terms is perceived as widespread.
Steve