I attempted to do my best for our identifier element, and part of how I came up with possible options for our project was examining what other universities used for identifier in their digital repositories.
First up, the University of Southern California Digital Library:
Some of the images in the digital library are from collaborating institutions, but most items are held by USC.
Their identifier label is “Record ID,” and the Record ID starts with a term denoting the collection it is a part of such as acsc for Automobile Club of Southern California or kda for Korean Digital Archives. This collection designation is followed by a dash, than the letter m followed by a number. I was unable to find the standard used to create this number, but it is likely either an asession number or an assigned number unique to each record in that particular collection.
Next up: Indiana University Digital Library Program
In their “Archives Photo Collection,” the images have THREE identifiers. One, “image number”, appears to be an assigned unique number. The second, donor image number, is the location of the photo on a CD, the third, accession number, is the year acquired and a sequential number separated by a period. The sequence comes from when the item is entered into record. So, 95/014 was acquired in 95 and was the 14th item entered.
And finally: The University of Missouri Digital Library, which has specific image collections, one of which is a collection of University of Missouri Sports Posters.
This collection’s label for identifier is “Identifier Image.” and the identifier is a very simple file name, picture1.jpg, picture2.jpg, and so on.
For photographs held by other organizations, such as those held by the Boone Historical Society, the collections are designated similar to SC, with a collection abbreviation (bchs) followed by an assigned ordered number. (bschs-0001, bsch-0002, etc.)
The university also adds an “other identifier” label, that is an ordered number.
Examining these universities is what led me to create the identifier element indexing guidelines many moons ago. A lot of times the research, learning, and bookmarking part happens, but something gets short-circuited between those steps and the blogging step!